fortran: Add -static-libquadmath support [PR46539]

The following patch is a revival of the
https://gcc.gnu.org/legacy-ml/gcc-patches/2014-10/msg00771.html
patch.  While trunk configured against recent glibc and with linker
--as-needed support doesn't really need to link against -lquadmath
anymore, there are still other targets where libquadmath is still in
use.
As has been discussed, making -static-libgfortran imply statically
linking both libgfortran and libquadmath is undesirable because of
the significant licensing differences between the 2 libraries.
Compared to the 2014 patch, this one doesn't handle -lquadmath
addition in the driver, which to me looks incorrect, libgfortran
configure determines where in libgfortran.spec -lquadmath should
be present if at all and with what it should be wrapped, but
analyzes gfortran -### -static-libgfortran stderr and based on
that figures out what gcc/configure.ac determined.

2022-08-17  Francois-Xavier Coudert  <fxcoudert@gcc.gnu.org>
	    Jakub Jelinek  <jakub@redhat.com>

	PR fortran/46539
gcc/
	* common.opt (static-libquadmath): New option.
	* gcc.cc (driver_handle_option): Always accept -static-libquadmath.
	* config/darwin.h (LINK_SPEC): Handle -static-libquadmath.
gcc/fortran/
	* lang.opt (static-libquadmath): New option.
	* invoke.texi (-static-libquadmath): Document it.
	* options.cc (gfc_handle_option): Error out if -static-libquadmath
	is passed but we do not support it.
libgfortran/
	* acinclude.m4 (LIBQUADSPEC): From $FC -static-libgfortran -###
	output determine -Bstatic/-Bdynamic, -bstatic/-bdynamic,
	-aarchive_shared/-adefault linker support or Darwin remapping
	of -lgfortran to libgfortran.a%s and use that around or instead
	of -lquadmath in LIBQUADSPEC.
	* configure: Regenerated.

Co-Authored-By: Francois-Xavier Coudert <fxcoudert@gcc.gnu.org>

3 files changed, 26 insertions, 1 deletions

diff --git a/gcc/fortran/invoke.texi b/gcc/fortran/invoke.texi
index c0932f6..4d1e0d6 100644
--- a/gcc/fortran/invoke.texi
+++ b/gcc/fortran/invoke.texi
@@ -170,7 +170,7 @@ and warnings}.
 
 @item Link Options
 @xref{Link Options,,Options for influencing the linking step}.
-@gccoptlist{-static-libgfortran}
+@gccoptlist{-static-libgfortran  -static-libquadmath}
 
 @item Runtime Options
 @xref{Runtime Options,,Options for influencing runtime behavior}.
@@ -1425,6 +1425,20 @@ configured, this option has no effect.
 @end table
 
 
+@table @gcctabopt
+@item -static-libquadmath
+@opindex @code{static-libquadmath}
+On systems that provide @file{libquadmath} as a shared and a static
+library, this option forces the use of the static version. If no
+shared version of @file{libquadmath} was built when the compiler was
+configured, this option has no effect.
+
+Please note that the @file{libquadmath} runtime library is licensed under the
+GNU Lesser General Public License (LGPL), and linking it statically introduces
+requirements when redistributing the resulting binaries.
+@end table
+
+
 @node Runtime Options
 @section Influencing runtime behavior
 @cindex options, runtime
diff --git a/gcc/fortran/lang.opt b/gcc/fortran/lang.opt
index cf39712..e8cd735 100644
--- a/gcc/fortran/lang.opt
+++ b/gcc/fortran/lang.opt
@@ -863,6 +863,10 @@ static-libgfortran
 Fortran
 Statically link the GNU Fortran helper library (libgfortran).
 
+static-libquadmath
+Fortran
+Statically link the GCC Quad-Precision Math Library (libquadmath).
+
 std=f2003
 Fortran
 Conform to the ISO Fortran 2003 standard.
diff --git a/gcc/fortran/options.cc b/gcc/fortran/options.cc
index d0fa634..38249d6 100644
--- a/gcc/fortran/options.cc
+++ b/gcc/fortran/options.cc
@@ -692,6 +692,13 @@ gfc_handle_option (size_t scode, const char *arg, HOST_WIDE_INT value,
 #endif
       break;
 
+    case OPT_static_libquadmath:
+#ifndef HAVE_LD_STATIC_DYNAMIC
+      gfc_fatal_error ("%<-static-libquadmath%> is not supported in this "
+		       "configuration");
+#endif
+      break;
+
     case OPT_fintrinsic_modules_path:
     case OPT_fintrinsic_modules_path_: