PR libstdc++/51296
	* testsuite/30_threads/thread/native_handle/typesizes.cc: Do not run
	on alpha*-*-osf*.
	* testsuite/30_threads/future/cons/constexpr.cc: Disable debug
	symbols.
	* testsuite/30_threads/shared_future/cons/constexpr.cc: Likewise.

From-SVN: r181740