[cr_tests] warning fixes and build system changes

[Serge E. Hallyn]

Quoting Nathan Lynch (ntl at pobox.com):
> Hi all,
> Patch summaries and overall diffstat below.  Please follow up here with
> any concerns, thanks!

Was it on purpose that you no longer delete the cr_* directories
with the test results on a 'make clean'?  If you're concerned about
accidentally losing info, then how about adding 'make distclean'
to do that?

-serge