shared: patch c-stdaux.h to not include <stdatomic.h>

c-stdaux is C11 and so is NetworkManager too.
But we build on Ubunut 14.04, where we have not all C11 parts
in place.

Since the header is not actually used (at the moment), patch out
the include.

shared/c-stdaux/src/c-stdaux.h

@@ -36,7 +36,9 @@ extern "C" {
 #include <limits.h>
 #include <stdalign.h>
 #include <stdarg.h>
+#if 0 /* NM_IGNORED */
 #include <stdatomic.h>
+#endif /* NM_IGNORED */
 #include <stdbool.h>
 #include <stddef.h>
 #include <stdio.h>