test: avoid false positives in 'cc-no-c-o' script

test: avoid false positives in 'cc-no-c-o' script

Fixes automake bug#14911.

* t/ax/cc-no-c-o.in: Be more careful in determining whether both the
'-c' and '-o' options have been passed on the command line to the
compiler.  In particular, do not spuriously complain in the face of
options like '-compatibility_version' or '-current_version' (seen on
Mac OS X 10.7).
* THANKS: Update.

Signed-off-by: Stefano Lattarini <stefano.lattarini@gmail.com>