Move base_machine and machine settings from configure.ac to sysdeps preconfigure...

Move base_machine and machine settings from configure.ac to sysdeps preconfigure fragments.

This patch makes non-ex-ports architectures set base_machine and
machine based on the original configured machine value in preconfigure
fragments, like ex-ports architectures, rather than in the toplevel
configure.ac.

Tested x86 that the disassembly of installed shared libraries is
unchanged by the patch.

	* configure.ac (base_machine): Do not set specially for particular
	machines here.
	* configure: Regenerated.
	* sysdeps/powerpc/preconfigure: Move machine and base_machine
	settings from configure.ac.
	* sysdeps/i386/preconfigure: New file.
	* sysdeps/s390/preconfigure: Likewise.
	* sysdeps/sh/preconfigure: Likewise.
	* sysdeps/sparc/preconfigure: Likewise.