[lumped builds] Only define _CRT_SECURE_NO_WARNINGS if it’s not defined yet.
When glslang is built with some other build system and lumped/unity builds are used,
without the checks this would get “macro is being redefined” warnings/errors.
diff --git a/StandAlone/StandAlone.cpp b/StandAlone/StandAlone.cpp
index 3faadec..76af8fe 100644
--- a/StandAlone/StandAlone.cpp
+++ b/StandAlone/StandAlone.cpp
@@ -35,7 +35,9 @@
//
// this only applies to the standalone wrapper, not the front end in general
+#ifndef _CRT_SECURE_NO_WARNINGS
#define _CRT_SECURE_NO_WARNINGS
+#endif
#include "ResourceLimits.h"
#include "Worklist.h"