modula2/108144 - fix --enable-version-specific-runtime-libs

modula2/108144 - fix --enable-version-specific-runtime-libs

The following fixes --enable-version-specific-runtime-libs for
the modula2 target libraries.  The issue is that the install
happens via for example

toolexeclib_LTLIBRARIES = libm2cor.la

and toolexeclibdir is set to $(toolexecdir)/$(gcc_version)$(MULTISUBDIR)
but the Makefile.am do not define $(gcc_version) but instead
$(version) which is used locally to define libsubdir.  The fix
is to consistently define and use $(gcc_version), also properly
supporting --with-gcc-major-version-only

	PR modula2/108144
libgm2/
	* configure.ac: Add GCC_BASE_VER.
	* configure: Re-generate.
	* Makefile.am: Use @get_gcc_base_ver@ for gcc_version.
	* libm2cor/Makefile.am: Likewise.  Use gcc_version instead
	of version.
	* libm2iso/Makefile.am: Likewise.
	* libm2log/Makefile.am: Likewise.
	* libm2min/Makefile.am: Likewise.
	* libm2pim/Makefile.am: Likewise.
	* Makefile.in: Re-generate.
	* libm2cor/Makefile.in: Likewise.
	* libm2iso/Makefile.in: Likewise.
	* libm2log/Makefile.in: Likewise.
	* libm2min/Makefile.in: Likewise.
	* libm2pim/Makefile.in: Likewise.