Add PowerMac support and many other enhancements.

	Add PowerMac support and many other enhancements.
	* mpw-configure: New option --cc to select compiler to use,
	paste options set according to --cc into the generated
	Makefile, generate the Makefile by sed'ing the Unix Makefile.in
	if mpw-make.sed is present.
	* mpw-config.in: Don't test for gC1, test for mpw-touch,
	add forward includes for PowerPC include files.
	* mpw-build.in: Build using Makefile.PPC if present.
	(do-byacc, etc): Remove separate version resource builds.
	(do-gas): Build "stamps" before "all".
	(do-gcc): Build "stamps-h" and "stamps-c" before "all".
	* mpw-README: Update to reflect --cc option, PowerMac support,
	and recently-reported compatibility problems.