* Makefile.def: Remove libstdcxx_incdir, libsubdir, gxx_include_dir,
gcc_version, and gcc_version_trigger from set of flags to pass.
* Makefile.tpl: Remove definitions of above variables.
(config.status): Remove dependency on $(gcc_version_trigger).
* Makefile.in: Regenerate.
* configure.in: Do not reference config/gcc-version.m4 nor
config/gxx-include-dir.m4. Do not invoke TL_AC_GCC_VERSION nor
TL_AC_GXX_INCLUDE_DIR. Do not set gcc_version_trigger.
* configure: Regenerate.
config:
* gxx-include-dir.m4: In all substitutions, leave $(gcc_version)
to be expanded by the Makefile.
