Only use __float128 in test if available

	* testsuite/26_numerics/complex/requirements/more_constexpr.cc: Fix
	failure on targets without __float128.

From-SVN: r266450

libstdc++-v3/ChangeLog

+2018-11-26  Jonathan Wakely  <jwakely@redhat.com>
+
+	* testsuite/26_numerics/complex/requirements/more_constexpr.cc: Fix
+	failure on targets without __float128.
+
 2018-11-23  Edward Smith-Rowland  <3dw4rd@verizon.net>
 
 	Implement P0415 More constexpr for std::complex.

libstdc++-v3/testsuite/26_numerics/complex/requirements/more_constexpr.cc

@@ -164,8 +164,10 @@ int main()
   __gnu_test::test_operator_members<long double, double>();
   __gnu_test::test_operator_members<long double, long double>();
 
+#if defined(_GLIBCXX_USE_FLOAT128)
   // Test primary template.
   __gnu_test::test_operator_members<__float128, __float128>();
+#endif
 
   return 0;
 }