Fix testsuite failures with --disable-wchar_t

Fix testsuite failures with --disable-wchar_t

	* testsuite/21_strings/basic_string/literals/types.cc: Guard use of
	wchar_t with _GLIBCXX_USE_WCHAR_T.
	* testsuite/21_strings/basic_string/literals/values.cc: Likewise.
	* testsuite/21_strings/basic_string/requirements/citerators.cc:
	Likewise.
	* testsuite/22_locale/messages/13631.cc: Likewise.
	* testsuite/experimental/string_view/literals/types.cc: Likewise.
	* testsuite/experimental/string_view/literals/values.cc: Likewise.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@228439 138bc75d-0d04-0410-961f-82ee72b054a4