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>

1 files changed, 4 insertions, 2 deletions

diff --git a/gcc/gcc.cc b/gcc/gcc.cc
index 75ca0ec..b6d562a 100644
--- a/gcc/gcc.cc
+++ b/gcc/gcc.cc
@@ -4585,12 +4585,14 @@ driver_handle_option (struct gcc_options *opts,
     case OPT_static_libgcc:
     case OPT_shared_libgcc:
     case OPT_static_libgfortran:
+    case OPT_static_libquadmath:
     case OPT_static_libphobos:
     case OPT_static_libstdc__:
       /* These are always valid, since gcc.cc itself understands the
 	 first two, gfortranspec.cc understands -static-libgfortran,
-	 d-spec.cc understands -static-libphobos, and g++spec.cc
-	 understands -static-libstdc++ */
+	 d-spec.cc understands -static-libphobos, g++spec.cc
+	 understands -static-libstdc++ and libgfortran.spec handles
+	 -static-libquadmath.  */
       validated = true;
       break;