PATCH: 4.0 backport of libstdc++ testsuite changes

[Benjamin Kosnik]

> I'm happy with leaving things alone; I just thought it might be nicer 
> not to have the overlap.  Anyhow, you should be aware that the DejaGNU 
> testsuite no longer pays any attention to the testsuite_thread file, 
> even though those are still created.

Cool. All I care about is testsuite_files and
testsuite_files_peformance. They still work, as long as I invoke the
extra make rules to create them. So, I'm ok with this arrangement. 

I don't care about tesuite_wchar_t or testsuite_thread. If they are no
longer being used at all, then their creation should be removed from
testsuite/Makefile.am to avoid confusion. If it's just testsuite_thread
that should be removed, then so be it.... 

Sound reasonable? Or, mostly reasonable?

-benjamin