PR libstdc++/83134
	* include/std/type_traits (__not_): Explicitly convert to bool.
	* testsuite/20_util/declval/requirements/1_neg.cc: Adjust dg-error.
	* testsuite/20_util/logical_traits/83134.cc: New test.
	* testsuite/20_util/make_signed/requirements/typedefs_neg.cc: Adjust
	dg-error.
	* testsuite/20_util/make_unsigned/requirements/typedefs_neg.cc:
	Likewise.

From-SVN: r255122