Use toplevel configure for GMP and MPFR for gdb

Use toplevel configure for GMP and MPFR for gdb

This patch uses the toplevel configure parts for GMP/MPFR for
gdb. The only thing is that gdb now requires MPFR for building.
Before it was a recommended but not required library.
Also this allows building of GMP and MPFR with the toplevel
directory just like how it is done for GCC.
We now error out in the toplevel configure of the version
of GMP and MPFR that is wrong.

OK after GDB 13 branches? Build gdb 3 ways:
with GMP and MPFR in the toplevel (static library used at that point for both)
With only MPFR in the toplevel (GMP distro library used and MPFR built from source)
With neither GMP and MPFR in the toplevel (distro libraries used)

Changes from v1:
* Updated gdb/README and gdb/doc/gdb.texinfo.
* Regenerated using unmodified autoconf-2.69

Thanks,
Andrew Pinski

ChangeLog:
	* Makefile.def: Add configure-gdb dependencies
	on all-gmp and all-mpfr.
	* configure.ac: Split out MPC checking from MPFR.
	Require GMP and MPFR if the gdb directory exist.
	* Makefile.in: Regenerate.
	* configure: Regenerate.

gdb/ChangeLog:

	PR bug/28500
	* configure.ac: Remove AC_LIB_HAVE_LINKFLAGS
	for gmp and mpfr.
	Use GMPLIBS and GMPINC which is provided by the
	toplevel configure.
	* Makefile.in (LIBGMP, LIBMPFR): Remove.
	(GMPLIBS, GMPINC): Add definition.
	(INTERNAL_CFLAGS_BASE): Add GMPINC.
	(CLIBS): Exchange LIBMPFR and LIBGMP
	for GMPLIBS.
	* target-float.c: Make the code conditional on
	HAVE_LIBMPFR unconditional.
	* top.c: Remove code checking HAVE_LIBMPFR.
	* configure: Regenerate.
	* config.in: Regenerate.
	* README: Update GMP/MPFR section of the config
	options.
	* doc/gdb.texinfo: Likewise.

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=28500