Additional check for bool header definition

src/raylib.h

@@ -296,9 +296,8 @@
 //----------------------------------------------------------------------------------
 #ifndef __cplusplus
 // Boolean type
-    #if !defined(_STDBOOL_H)
+    #if !defined(_STDBOOL_H) || !defined(__STDBOOL_H)   // CLang uses second form
         typedef enum { false, true } bool;
-        #define _STDBOOL_H
     #endif
 #endif