Add build-many-glibcs.py option to strip installed shared libraries.

This patch adds a --strip option to build-many-glibcs.py, to make it
strip the installed shared libraries after installation.  This is for
convenience if you want to compare installed stripped shared libraries
before and after a patch that was not meant to result in any code
changes: you can run with this option, copy the install/glibcs
directory, run again with the patch and compare the */lib*
subdirectory contents.

(It might make sense for the option to strip libraries in other
directories, including stripping debug information from static
libraries, with a view to making it possible for a
no-generated-code-changes patch to result in completely identical
install/glibcs directories, so simplifying comparison, though that may
need other build determinism changes, e.g. to build deterministic .a
files.)

	* scripts/build-many-glibcs.py (Context.__init__): Take strip
	argument.
	(Glibc.build_glibc): Strip installed shared libraries if
	requested.
	(get_parser): Add --strip option.
	(main): Update Context call.