Guard against DEBUG Redefinition

Undefine DEBUG to avoid external redefinition
warnings/conflicts.  This is probably a common
definition for many external build systems'
debug configurations.

This ensures raylib will not emit
a warning about the DEBUG definition being
redefined in external build systems.

Author: NiamhNightglow

src/external/jar_xm.h

@@ -230,8 +230,16 @@ uint64_t jar_xm_get_remaining_samples(jar_xm_context_t* ctx);
 #include <stdio.h>
 #include <stdlib.h>
 #include <limits.h>
+
 #include <string.h>
 
+#ifdef DEBUG
+    // Undefine DEBUG to avoid external redefinition warnings/conflicts
+    // This is probably a common definition for
+    // many external build systems' debug configurations
+    #undef DEBUG
+#endif
+
 #if JAR_XM_DEBUG            //JAR_XM_DEBUG defined as 0
 #include <stdio.h>
 #define DEBUG(fmt, ...) do {                                        \