libiberty: autogenerate aclocal.m4

Move custom macros to acinclude.m4 so we can autogenerate aclocal.m4
with aclocal.  This matches every other project in the tree.

libiberty/ChangeLog:

	* Makefile.in (ACLOCAL, ACLOCAL_AMFLAGS, $(srcdir)/aclocal.m4): Define.
	(configure_deps): Rename to ...
	(aclocal_deps): ... this.  Replace aclocal.m4 with acinclude.m4.
	($(srcdir)/configure): Replace $(configure_deps) with
	$(srcdir)/aclocal.m4.
	* aclocal.m4: Move libiberty macros to acinclude.m4, then regenerate.
	* acinclude.m4: New file.
	* configure: Regenerate.