Add build-many-glibcs.py --enable-obsolete-* configs.

Add build-many-glibcs.py --enable-obsolete-* configs.

We've had issues before with build failures (with new GCC) in code
only built with --enable-obsolete-rpc or --enable-obsolete-nsl not
being reported for a while because build-many-glibcs.py does not test
those configure options.  This patch adds configurations (32-bit and
64-bit) using those options so that in future we can notice quickly if
they start failing to build.

Tested the new configurations do build with GCC 8.

	* scripts/build-many-glibcs.py (Context.add_all_configs): Add
	x86_64 and i686 configs using --enable-obsolete-rpc
	--enable-obsolete-nsl.