gcc.misc-tests/outputs.exp: assert unique test-names

gcc.misc-tests/outputs.exp: assert unique test-names

The gcc.misc-tests/outputs.exp tests can take some effort to
digest.

Navigating and debugging causes for failing tests here isn't
helped by the existence of tests with duplicate names.
Let's stop that from happening.  This requires that test-run
output is actually reviewed, as Tcl errors don't stop the
test-run, but then again there's no such dejagnu construct
that I know of.

Tested x86_64-pc-linux-gnu.

gcc/testsuite:
	* gcc.misc-tests/outputs.exp: Append discriminating
	suffixes to tests with duplicate names.
	(outest): Assert that each running test has a unique
	name.