Add #[cfg(debug)] flag to rust suite compilation. Closes #3068

Author: z0w0

Makefile.in

@@ -101,7 +101,7 @@ endif
 
 ifdef CFG_ENABLE_DEBUG
   $(info cfg: enabling more debugging (CFG_ENABLE_DEBUG))
-  CFG_RUSTC_FLAGS +=
+  CFG_RUSTC_FLAGS += --cfg debug
   CFG_GCCISH_CFLAGS += -DRUST_DEBUG
 else
   CFG_GCCISH_CFLAGS += -DRUST_NDEBUG