Silence warning in MSVC about VLAs.

When janet.h is included as a C++ header in
MSVC, shows warnings.

src/include/janet.h

@@ -27,6 +27,12 @@
 extern "C" {
 #endif
 
+/* Variable length arrays are ok */
+#ifdef _MSC_VER
+#pragma warning( push )
+#pragma warning( disable : 4200 )
+#endif
+
 /***** START SECTION CONFIG *****/
 
 #include "janetconf.h"
@@ -1652,6 +1658,11 @@ JANET_API int janet_thread_send(JanetThread *thread, Janet msg, double timeout);
 
 /***** END SECTION MAIN *****/
 
+/* Re-enable popped variable length array warnings */
+#ifdef _MSC_VER
+#pragma warning( pop )
+#endif
+
 #ifdef __cplusplus
 }
 #endif