update DBG_DISCARD macro to allow the compiler to see the argument for compile-time checking, while still having it optimized away during compilation

src/include/compiler.h

 #endif
 
 #define DBG_PRINT(...) printf ( __VA_ARGS__ )
-#define DBG_DISCARD(...) do {} while ( 0 )
+#define DBG_DISCARD(...) do { if ( 0 ) printf ( __VA_ARGS__ ); } while ( 0 )
+/*#define DBG_DISCARD(...) do {} while ( 0 )*/
+
 #define DBG  DBG_DISCARD
 #define DBG2 DBG_DISCARD