libstdc++: Make operator== for std::tuple convert to bool [PR119545]

libstdc++: Make operator== for std::tuple convert to bool [PR119545]

The boolean-testable requirements don't require the type to be copyable,
so we need to convert to bool before it might need to be copied.

libstdc++-v3/ChangeLog:

	PR libstdc++/119545
	* include/std/tuple (operator==): Convert comparison results to
	bool.
	* testsuite/20_util/tuple/comparison_operators/119545.cc: New
	test.

Reviewed-by: Tomasz Kamiński <tkaminsk@redhat.com>