Update conditional for C11 atomics to use HAVE_C11
@@ -681,7 +681,7 @@ __declspec(dllimport) int __cdecl omp_in_parallel(void);
__declspec(dllimport) int __cdecl omp_get_num_procs(void);
#endif
-#if (__STDC_VERSION__ >= 201112L)
+#ifdef HAVE_C11
#if defined(C_GCC) && ( __GNUC__ < 7)
// workaround for GCC bug 65467
#ifndef _Atomic
