Define NDEBUG for RELEASE builds

We don't want our assertions asserting.

src/build/Common.gmake

@@ -524,7 +524,7 @@ ifdef DEBUG
 else # RELEASE
  # -finline-functions (used to) break the baja build badly.
  # This also meant that -O3 wouldn't work either.
- CFLAGS	:= -O3 -Wno-unused-result -ffast-math -funroll-loops $(CFLAGS)
+ CFLAGS	:= -O3 -Wno-unused-result -ffast-math -funroll-loops $(CFLAGS) -DNDEBUG
  ifndef NO_LTO
   # Not Yet... this requires more care with library ordering.
   # CFLAGS += -flto