The libstdc++ testsuite only runs .cc files, so these two old tests have
never been run.

Signed-off-by: Jonathan Wakely <jwakely@redhat.com>

libstdc++-v3/ChangeLog:

	* testsuite/26_numerics/valarray/dr630-3.C: Moved to...
	* testsuite/26_numerics/valarray/dr630-3.cc: ...here.
	* testsuite/27_io/basic_iostream/cons/16251.C: Moved to...
	* testsuite/27_io/basic_iostream/cons/16251.cc: ...here.

Tested x86_64-linux. Committed to trunk.