libstdc++: Optimize std::is_trivially_destructible_v

This reduces the overhead of using std::is_trivially_destructible_v and
as a result fixes some recent regressions seen with a non-default
GLIBCXX_TESTSUITE_STDS env var:
FAIL: 20_util/variant/87619.cc  -std=gnu++20 (test for excess errors)
FAIL: 20_util/variant/87619.cc  -std=gnu++23 (test for excess errors)
FAIL: 20_util/variant/87619.cc  -std=gnu++26 (test for excess errors)

libstdc++-v3/ChangeLog:

	* include/std/type_traits (is_trivially_destructible_v): Use
	built-in directly when concepts are supported.
	* testsuite/20_util/is_trivially_destructible/value_v.cc: New
	test.