Make 'autoreconf' work for 'gcc', 'libobjc'

Make 'autoreconf' work for 'gcc', 'libobjc'

With that, we may then run plain 'autoreconf' for all of GCC's subpackages,
instead of for some of those (that don't use Automake) manually having to run
the applicable combination of 'aclocal', 'autoconf', 'autoheader'.

See also 'AC_CONFIG_MACRO_DIRS'/'AC_CONFIG_MACRO_DIR' usage elsewhere.

	gcc/
	* configure.ac (AC_CONFIG_MACRO_DIRS): Instantiate.
	* configure: Regenerate.
	libobjc/
	* configure.ac (AC_CONFIG_MACRO_DIRS): Instantiate.
	* configure: Regenerate.