Add build-many-glibcs.py powerpc-linux-gnu-power4 build.

The 32-bit powerpc configurations in build-many-glibcs.py were failing
to cover the powerpc32 multiarch code at all, because that code is
only built for power4 and above configurations.  This patch adds a
32-bit power4 configuration so that at least some of that multiarch
code gets build-tested.  (This is preparation for reviewing the w_*
file renaming, which affects such powerpc32 multiarch files.)

	* scripts/build-many-glibcs.py (Context.add_all_configs): Add
	power4 glibc for powerpc-linux-gnu.