Fix atomic_win32.h for VS2015
VS2015 issues this:
atomic_win32.h(32): error: expected a ")"
atomic_win32.h(32): error: expected an identifier
atomic_win32.h(32): error: expected a ";"
@@ -29,7 +29,7 @@ namespace __atomic {
template <typename _Tp> _Tp __create();
template <typename _Tp, typename _Td>
-enable_if_t<sizeof(_Tp() = __create<_Td>()), char>
+enable_if_t<sizeof(__create<_Tp>() = __create<_Td>()), char>
__test_atomic_assignable(int);
template <typename _Tp, typename _Up>
__two __test_atomic_assignable(...);
