Add C dialect reminders to each source file
Files built for Win32 must use C89 style declarations for compatibility
with VS 2010 and 2012, which are still supported by GLFW.
diff --git a/src/null_joystick.c b/src/null_joystick.c
index bcd4b80..36c18aa 100644
--- a/src/null_joystick.c
+++ b/src/null_joystick.c
@@ -23,6 +23,8 @@
// distribution.
//
//========================================================================
+// It is fine to use C99 in this file because it will not be built with VS
+//========================================================================
#include "internal.h"
