Enable WHISPER_DEBUG flag to get DEBUG logs on debug builds

sys/build.rs

@@ -184,6 +184,7 @@ fn main() {
         // debug builds are too slow to even remotely be usable,
         // so we build with optimizations even in debug mode
         config.define("CMAKE_BUILD_TYPE", "RelWithDebInfo");
+        config.cxxflag("-DWHISPER_DEBUG");
     }
 
     // Allow passing any WHISPER cmake flag