Update ax_cv_cxx_compile_cxx.m4

This file provides the AX_CXX_COMPILE_STDCXX macro.  In the context of
the following patch, I wanted to build and test GDB in c++17 mode.  The
version of the macro we have in the repo does not support detecting
c++17 compilers, but the upstream version has been updated to do so.

Since we have local modifications to the file, I had to reconcile our
modifications and the updated upstream version (which was relatively
straightforward).

gdb/ChangeLog:

	* ax_cxx_compile_stdcxx.m4: Sync with upstream.
	* configure: Re-generate.

3 files changed, 460 insertions, 31 deletions

diff --git a/gdb/ChangeLog b/gdb/ChangeLog
index 71e175f..f398139 100644
--- a/gdb/ChangeLog
+++ b/gdb/ChangeLog
@@ -1,3 +1,8 @@
+2018-04-09  Simon Marchi  <simon.marchi@polymtl.ca>
+
+	* ax_cxx_compile_stdcxx.m4: Sync with upstream.
+	* configure: Re-generate.
+
 2018-04-09  Pedro Alves  <palves@redhat.com>
 
 	* gdbarch.sh: Include "observable.h" instead of "observer.h".
diff --git a/gdb/ax_cxx_compile_stdcxx.m4 b/gdb/ax_cxx_compile_stdcxx.m4
index 444799a..9a9e9e7 100644
--- a/gdb/ax_cxx_compile_stdcxx.m4
+++ b/gdb/ax_cxx_compile_stdcxx.m4
@@ -8,7 +8,7 @@
 # - AC_SUBST CXX_DIALECT instead of changing CXX/CXXCPP.
 #
 # ===========================================================================
-#   http://www.gnu.org/software/autoconf-archive/ax_cxx_compile_stdcxx.html
+#  https://www.gnu.org/software/autoconf-archive/ax_cxx_compile_stdcxx.html
 # ===========================================================================
 #
 # SYNOPSIS
@@ -42,21 +42,22 @@
 #   Copyright (c) 2014, 2015 Google Inc.; contributed by Alexey Sokolov <sokolov@google.com>
 #   Copyright (c) 2015 Paul Norman <penorman@mac.com>
 #   Copyright (c) 2015 Moritz Klammler <moritz@klammler.eu>
+#   Copyright (c) 2016 Krzesimir Nowak <qdlacz@gmail.com>
 #
 #   Copying and distribution of this file, with or without modification, are
 #   permitted in any medium without royalty provided the copyright notice
 #   and this notice are preserved.  This file is offered as-is, without any
 #   warranty.
 
-#serial 4
+#serial 8
 
 dnl  This macro is based on the code from the AX_CXX_COMPILE_STDCXX_11 macro
 dnl  (serial version number 13).
 
 AC_DEFUN([AX_CXX_COMPILE_STDCXX], [dnl
-  m4_if([$1], [11], [],
-        [$1], [14], [],
-        [$1], [17], [m4_fatal([support for C++17 not yet implemented in AX_CXX_COMPILE_STDCXX])],
+  m4_if([$1], [11], [ax_cxx_compile_alternatives="11 0x"],
+        [$1], [14], [ax_cxx_compile_alternatives="14 1y"],
+        [$1], [17], [ax_cxx_compile_alternatives="17 1z"],
         [m4_fatal([invalid first argument `$1' to AX_CXX_COMPILE_STDCXX])])dnl
   m4_if([$2], [], [],
         [$2], [ext], [],
@@ -80,7 +81,8 @@ AC_DEFUN([AX_CXX_COMPILE_STDCXX], [dnl
 
   m4_if([$2], [noext], [], [dnl
   if test x$ac_success = xno; then
-    for switch in -std=gnu++$1 -std=gnu++0x; do
+    for alternative in ${ax_cxx_compile_alternatives}; do
+      switch="-std=gnu++${alternative}"
       cachevar=AS_TR_SH([ax_cv_cxx_compile_cxx$1_$switch])
       AC_CACHE_CHECK(whether $CXX supports C++$1 features with $switch,
                      $cachevar,
@@ -103,19 +105,24 @@ AC_DEFUN([AX_CXX_COMPILE_STDCXX], [dnl
     dnl HP's aCC needs +std=c++11 according to:
     dnl http://h21007.www2.hp.com/portal/download/files/unprot/aCxx/PDF_Release_Notes/769149-001.pdf
     dnl Cray's crayCC needs "-h std=c++11"
-    for switch in -std=c++$1 -std=c++0x +std=c++$1 "-h std=c++$1"; do
-      cachevar=AS_TR_SH([ax_cv_cxx_compile_cxx$1_$switch])
-      AC_CACHE_CHECK(whether $CXX supports C++$1 features with $switch,
-                     $cachevar,
-        [ac_save_CXX="$CXX"
-         CXX="$CXX $switch"
-         AC_COMPILE_IFELSE([AC_LANG_SOURCE([_AX_CXX_COMPILE_STDCXX_testbody_$1])],
-          [eval $cachevar=yes],
-          [eval $cachevar=no])
-         CXX="$ac_save_CXX"])
-      if eval test x\$$cachevar = xyes; then
-        CXX_DIALECT="$switch"
-        ac_success=yes
+    for alternative in ${ax_cxx_compile_alternatives}; do
+      for switch in -std=c++${alternative} +std=c++${alternative} "-h std=c++${alternative}"; do
+        cachevar=AS_TR_SH([ax_cv_cxx_compile_cxx$1_$switch])
+        AC_CACHE_CHECK(whether $CXX supports C++$1 features with $switch,
+                       $cachevar,
+          [ac_save_CXX="$CXX"
+           CXX="$CXX $switch"
+           AC_COMPILE_IFELSE([AC_LANG_SOURCE([_AX_CXX_COMPILE_STDCXX_testbody_$1])],
+            [eval $cachevar=yes],
+            [eval $cachevar=no])
+           CXX="$ac_save_CXX"])
+        if eval test x\$$cachevar = xyes; then
+          CXX_DIALECT="$switch"
+          ac_success=yes
+          break
+        fi
+      done
+      if test x$ac_success = xyes; then
         break
       fi
     done
@@ -153,6 +160,11 @@ m4_define([_AX_CXX_COMPILE_STDCXX_testbody_14],
   _AX_CXX_COMPILE_STDCXX_testbody_new_in_14
 )
 
+m4_define([_AX_CXX_COMPILE_STDCXX_testbody_17],
+  _AX_CXX_COMPILE_STDCXX_testbody_new_in_11
+  _AX_CXX_COMPILE_STDCXX_testbody_new_in_14
+  _AX_CXX_COMPILE_STDCXX_testbody_new_in_17
+)
 
 dnl  Tests for new features in C++11
 
@@ -523,7 +535,7 @@ namespace cxx14
 
   }
 
-  namespace test_digit_seperators
+  namespace test_digit_separators
   {
 
     constexpr auto ten_million = 100'000'000;
@@ -565,3 +577,409 @@ namespace cxx14
 #endif  // __cplusplus >= 201402L
 
 ]])
+
+
+dnl  Tests for new features in C++17
+
+m4_define([_AX_CXX_COMPILE_STDCXX_testbody_new_in_17], [[
+
+// If the compiler admits that it is not ready for C++17, why torture it?
+// Hopefully, this will speed up the test.
+
+#ifndef __cplusplus
+
+#error "This is not a C++ compiler"
+
+#elif __cplusplus <= 201402L
+
+#error "This is not a C++17 compiler"
+
+#else
+
+#if defined(__clang__)
+  #define REALLY_CLANG
+#else
+  #if defined(__GNUC__)
+    #define REALLY_GCC
+  #endif
+#endif
+
+#include <initializer_list>
+#include <utility>
+#include <type_traits>
+
+namespace cxx17
+{
+
+#if !defined(REALLY_CLANG)
+  namespace test_constexpr_lambdas
+  {
+
+    // TODO: test it with clang++ from git
+
+    constexpr int foo = [](){return 42;}();
+
+  }
+#endif // !defined(REALLY_CLANG)
+
+  namespace test::nested_namespace::definitions
+  {
+
+  }
+
+  namespace test_fold_expression
+  {
+
+    template<typename... Args>
+    int multiply(Args... args)
+    {
+      return (args * ... * 1);
+    }
+
+    template<typename... Args>
+    bool all(Args... args)
+    {
+      return (args && ...);
+    }
+
+  }
+
+  namespace test_extended_static_assert
+  {
+
+    static_assert (true);
+
+  }
+
+  namespace test_auto_brace_init_list
+  {
+
+    auto foo = {5};
+    auto bar {5};
+
+    static_assert(std::is_same<std::initializer_list<int>, decltype(foo)>::value);
+    static_assert(std::is_same<int, decltype(bar)>::value);
+  }
+
+  namespace test_typename_in_template_template_parameter
+  {
+
+    template<template<typename> typename X> struct D;
+
+  }
+
+  namespace test_fallthrough_nodiscard_maybe_unused_attributes
+  {
+
+    int f1()
+    {
+      return 42;
+    }
+
+    [[nodiscard]] int f2()
+    {
+      [[maybe_unused]] auto unused = f1();
+
+      switch (f1())
+      {
+      case 17:
+        f1();
+        [[fallthrough]];
+      case 42:
+        f1();
+      }
+      return f1();
+    }
+
+  }
+
+  namespace test_extended_aggregate_initialization
+  {
+
+    struct base1
+    {
+      int b1, b2 = 42;
+    };
+
+    struct base2
+    {
+      base2() {
+        b3 = 42;
+      }
+      int b3;
+    };
+
+    struct derived : base1, base2
+    {
+        int d;
+    };
+
+    derived d1 {{1, 2}, {}, 4};  // full initialization
+    derived d2 {{}, {}, 4};      // value-initialized bases
+
+  }
+
+  namespace test_general_range_based_for_loop
+  {
+
+    struct iter
+    {
+      int i;
+
+      int& operator* ()
+      {
+        return i;
+      }
+
+      const int& operator* () const
+      {
+        return i;
+      }
+
+      iter& operator++()
+      {
+        ++i;
+        return *this;
+      }
+    };
+
+    struct sentinel
+    {
+      int i;
+    };
+
+    bool operator== (const iter& i, const sentinel& s)
+    {
+      return i.i == s.i;
+    }
+
+    bool operator!= (const iter& i, const sentinel& s)
+    {
+      return !(i == s);
+    }
+
+    struct range
+    {
+      iter begin() const
+      {
+        return {0};
+      }
+
+      sentinel end() const
+      {
+        return {5};
+      }
+    };
+
+    void f()
+    {
+      range r {};
+
+      for (auto i : r)
+      {
+        [[maybe_unused]] auto v = i;
+      }
+    }
+
+  }
+
+  namespace test_lambda_capture_asterisk_this_by_value
+  {
+
+    struct t
+    {
+      int i;
+      int foo()
+      {
+        return [*this]()
+        {
+          return i;
+        }();
+      }
+    };
+
+  }
+
+  namespace test_enum_class_construction
+  {
+
+    enum class byte : unsigned char
+    {};
+
+    byte foo {42};
+
+  }
+
+  namespace test_constexpr_if
+  {
+
+    template <bool cond>
+    int f ()
+    {
+      if constexpr(cond)
+      {
+        return 13;
+      }
+      else
+      {
+        return 42;
+      }
+    }
+
+  }
+
+  namespace test_selection_statement_with_initializer
+  {
+
+    int f()
+    {
+      return 13;
+    }
+
+    int f2()
+    {
+      if (auto i = f(); i > 0)
+      {
+        return 3;
+      }
+
+      switch (auto i = f(); i + 4)
+      {
+      case 17:
+        return 2;
+
+      default:
+        return 1;
+      }
+    }
+
+  }
+
+#if !defined(REALLY_CLANG)
+  namespace test_template_argument_deduction_for_class_templates
+  {
+
+    // TODO: test it with clang++ from git
+
+    template <typename T1, typename T2>
+    struct pair
+    {
+      pair (T1 p1, T2 p2)
+        : m1 {p1},
+          m2 {p2}
+      {}
+
+      T1 m1;
+      T2 m2;
+    };
+
+    void f()
+    {
+      [[maybe_unused]] auto p = pair{13, 42u};
+    }
+
+  }
+#endif // !defined(REALLY_CLANG)
+
+  namespace test_non_type_auto_template_parameters
+  {
+
+    template <auto n>
+    struct B
+    {};
+
+    B<5> b1;
+    B<'a'> b2;
+
+  }
+
+#if !defined(REALLY_CLANG)
+  namespace test_structured_bindings
+  {
+
+    // TODO: test it with clang++ from git
+
+    int arr[2] = { 1, 2 };
+    std::pair<int, int> pr = { 1, 2 };
+
+    auto f1() -> int(&)[2]
+    {
+      return arr;
+    }
+
+    auto f2() -> std::pair<int, int>&
+    {
+      return pr;
+    }
+
+    struct S
+    {
+      int x1 : 2;
+      volatile double y1;
+    };
+
+    S f3()
+    {
+      return {};
+    }
+
+    auto [ x1, y1 ] = f1();
+    auto& [ xr1, yr1 ] = f1();
+    auto [ x2, y2 ] = f2();
+    auto& [ xr2, yr2 ] = f2();
+    const auto [ x3, y3 ] = f3();
+
+  }
+#endif // !defined(REALLY_CLANG)
+
+#if !defined(REALLY_CLANG)
+  namespace test_exception_spec_type_system
+  {
+
+    // TODO: test it with clang++ from git
+
+    struct Good {};
+    struct Bad {};
+
+    void g1() noexcept;
+    void g2();
+
+    template<typename T>
+    Bad
+    f(T*, T*);
+
+    template<typename T1, typename T2>
+    Good
+    f(T1*, T2*);
+
+    static_assert (std::is_same_v<Good, decltype(f(g1, g2))>);
+
+  }
+#endif // !defined(REALLY_CLANG)
+
+  namespace test_inline_variables
+  {
+
+    template<class T> void f(T)
+    {}
+
+    template<class T> inline T g(T)
+    {
+      return T{};
+    }
+
+    template<> inline void f<>(int)
+    {}
+
+    template<> int g<>(int)
+    {
+      return 5;
+    }
+
+  }
+
+}  // namespace cxx17
+
+#endif  // __cplusplus <= 201402L
+
+]])
diff --git a/gdb/configure b/gdb/configure
index f2acc1b..b313152 100755
--- a/gdb/configure
+++ b/gdb/configure
@@ -4967,7 +4967,7 @@ program_transform_name=`$as_echo "$program_transform_name" | sed "$ac_script"`
 # We require a C++11 compiler.  Check if one is available, and if
 # necessary, set CXX_DIALECT to some -std=xxx switch.
 
-      ax_cxx_compile_cxx11_required=true
+  ax_cxx_compile_alternatives="11 0x"    ax_cxx_compile_cxx11_required=true
   ac_ext=cpp
 ac_cpp='$CXXCPP $CPPFLAGS'
 ac_compile='$CXX -c $CXXFLAGS $CPPFLAGS conftest.$ac_ext >&5'
@@ -5283,7 +5283,8 @@ $as_echo "$ax_cv_cxx_compile_cxx11" >&6; }
   fi
 
     if test x$ac_success = xno; then
-    for switch in -std=gnu++11 -std=gnu++0x; do
+    for alternative in ${ax_cxx_compile_alternatives}; do
+      switch="-std=gnu++${alternative}"
       cachevar=`$as_echo "ax_cv_cxx_compile_cxx11_$switch" | $as_tr_sh`
       { $as_echo "$as_me:${as_lineno-$LINENO}: checking whether $CXX supports C++11 features with $switch" >&5
 $as_echo_n "checking whether $CXX supports C++11 features with $switch... " >&6; }
@@ -5601,16 +5602,17 @@ $as_echo "$ac_res" >&6; }
   fi
 
     if test x$ac_success = xno; then
-                for switch in -std=c++11 -std=c++0x +std=c++11 "-h std=c++11"; do
-      cachevar=`$as_echo "ax_cv_cxx_compile_cxx11_$switch" | $as_tr_sh`
-      { $as_echo "$as_me:${as_lineno-$LINENO}: checking whether $CXX supports C++11 features with $switch" >&5
+                for alternative in ${ax_cxx_compile_alternatives}; do
+      for switch in -std=c++${alternative} +std=c++${alternative} "-h std=c++${alternative}"; do
+        cachevar=`$as_echo "ax_cv_cxx_compile_cxx11_$switch" | $as_tr_sh`
+        { $as_echo "$as_me:${as_lineno-$LINENO}: checking whether $CXX supports C++11 features with $switch" >&5
 $as_echo_n "checking whether $CXX supports C++11 features with $switch... " >&6; }
 if { as_var=$cachevar; eval "test \"\${$as_var+set}\" = set"; }; then :
   $as_echo_n "(cached) " >&6
 else
   ac_save_CXX="$CXX"
-         CXX="$CXX $switch"
-         cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+           CXX="$CXX $switch"
+           cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 
 
@@ -5905,14 +5907,18 @@ else
   eval $cachevar=no
 fi
 rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
-         CXX="$ac_save_CXX"
+           CXX="$ac_save_CXX"
 fi
 eval ac_res=\$$cachevar
 	       { $as_echo "$as_me:${as_lineno-$LINENO}: result: $ac_res" >&5
 $as_echo "$ac_res" >&6; }
-      if eval test x\$$cachevar = xyes; then
-        CXX_DIALECT="$switch"
-        ac_success=yes
+        if eval test x\$$cachevar = xyes; then
+          CXX_DIALECT="$switch"
+          ac_success=yes
+          break
+        fi
+      done
+      if test x$ac_success = xyes; then
         break
       fi
     done