Disable unknown warning warning on !gcc

src/build/Common.gmake

@@ -451,7 +451,10 @@ endif
 ifdef DEBUG
  CFLAGS	+=	-ggdb
  CFLAGS	+=	-D_DEBUG
- CFLAGS +=	-Wall -Wno-char-subscripts -Wno-format-truncation
+ CFLAGS +=	-Wall -Wno-char-subscripts
+ ifeq ($(CCPRE),gcc)
+  CFLAGS +=	-Wno-format-truncation
+ endif
 else # RELEASE
  # -finline-functions (used to) break the baja build badly.
  # This also meant that -O3 wouldn't work either.