Remove powerpc special cases in configure.ac.

Remove powerpc special cases in configure.ac.

This patch removes two powerpc special cases in the main configure.ac.
The test for rs6000 is irrelevant to currently supported
configurations (config.guess reports rs6000 for some OSes, of which
the only one currently supported by GCC is AIX, but not for Linux).
There's no need either for a special case for powerpc*-*soft;
--without-fp suffices, and GCC doesn't have any special handling of
such a triplet.

Not tested.

	* configure.ac: Do not test for machine being rs6000.  Do not test
	for powerpc*-*soft.
	* configure: Regenerated.