testsuite, objective-c: Fix duplicate test names in 'special'.

testsuite, objective-c: Fix duplicate test names in 'special'.

For macOS/Darwin, we run Objective-C tests for both the GNU and
NeXT runtimes (and these runs are usually differentiated by
identifying the runtime in the test name).

However, the 'special' sub-set of tests had a non-standard driver
since it needs two sources for each test (but did not report the
runtime in the test name and so shows duplicates).

We can now automate the multi-source case with dg-additional-sources
but need to do a little work to filter these additional sources
from the set (since they also have a .m suffix).

This addresses the FIXME in the original driver.

To resolve the duplicated names, means amending the reported name
to include the runtime as a differentiator, this means that test
comparisons will temporarily report new and missing tests for any
comparison that includes this change.

gcc/testsuite/ChangeLog:

	* objc.dg/special/load-category-1.m: Add second source.
	* objc.dg/special/load-category-2.m: Likewise.
	* objc.dg/special/load-category-3.m: Likewise.
	* objc.dg/special/unclaimed-category-1.m: Likewise.
	* objc.dg/special/special.exp: Rewrite to make use of generic
	testsuite facilities.

Signed-off-by: Iain Sandoe <iain@sandoe.co.uk>