Add SPARC --disable-multi-arch builds to build-many-glibcs.py.

While working on SPARC changes to use libm_alias_* I noticed that the
non-multi-arch sparc32/sparcv9/fpu/s_fabs.S was missing compat symbol
support for fabsl.  This clearly shows inadequate test coverage, so
this patch adds SPARC --disable-multi-arch builds to
build-many-glibcs.py (the 32-bit one fails testing until that bug is
fixed, the 64-bit one passes testing).

	* scripts/build-many-glibcs.py (Context.add_all_configs): Add
	SPARC --disable-multi-arch glibc variants.