Poison non-POD memset & non-trivially-copyable memcpy/memmove

This patch catches invalid initialization of non-POD types with
memset, at compile time.

This is what I used to catch the problems fixed by the previous
patches in the series:

  $ make -k 2>&1 | grep "deleted function"
  src/gdb/breakpoint.c:951:53: error: use of deleted function ‘void* memset(T*, int, size_t) [with T = bp_location; <template-parameter-1-2> = void; size_t = long unsigned int]’
  src/gdb/breakpoint.c:7325:32: error: use of deleted function ‘void* memset(T*, int, size_t) [with T = bp_location; <template-parameter-1-2> = void; size_t = long unsigned int]’
  src/gdb/btrace.c:1153:42: error: use of deleted function ‘void* memset(T*, int, size_t) [with T = btrace_insn; <template-parameter-1-2> = void; size_t = long unsigned int]’
...

gdb/ChangeLog:
2017-04-25  Pedro Alves  <palves@redhat.com>

	* common/common-defs.h: Include "common/poison.h".
	* common/function-view.h: (Not, Or, Requires): Move to traits.h
	and adjust.
	* common/poison.h: New file.
	* common/traits.h: Include <type_traits>.
	(Not, Or, Requires): New, moved from common/function-view.h.

1 files changed, 29 insertions, 1 deletions

diff --git a/gdb/common/traits.h b/gdb/common/traits.h
index c8f29cc..4f7161b 100644
--- a/gdb/common/traits.h
+++ b/gdb/common/traits.h
@@ -32,7 +32,32 @@ template<typename... Ts>
 using void_t = typename make_void<Ts...>::type;
 
 /* A few trait helpers, mainly stolen from libstdc++.  Uppercase
-   because "and" is a keyword.  */
+   because "and/or", etc. are reserved keywords.  */
+
+template<typename Predicate>
+struct Not : public std::integral_constant<bool, !Predicate::value>
+{};
+
+template<typename...>
+struct Or;
+
+template<>
+struct Or<> : public std::false_type
+{};
+
+template<typename B1>
+struct Or<B1> : public B1
+{};
+
+template<typename B1, typename B2>
+struct Or<B1, B2>
+  : public std::conditional<B1::value, B1, B2>::type
+{};
+
+template<typename B1,typename B2,typename B3, typename... Bn>
+struct Or<B1, B2, B3, Bn...>
+  : public std::conditional<B1::value, B1, Or<B2, B3, Bn...>>::type
+{};
 
 template<typename...>
 struct And;
@@ -55,6 +80,9 @@ struct And<B1, B2, B3, Bn...>
   : public std::conditional<B1::value, And<B2, B3, Bn...>, B1>::type
 {};
 
+/* Concepts-light-like helper to make SFINAE logic easier to read.  */
+template<typename Condition>
+using Requires = typename std::enable_if<Condition::value, void>::type;
 }
 
 #endif /* COMMON_TRAITS_H */