Pass variables to submake

[Chenfu.Wang]

Hi, all,

I'd like to override submake's CPPFLAGS when I run "make debug" at the top 
level. I've tried in my top level Makefile, for example:

...
debug:
        export CPPFLAGS=-g
        $(MAKE) -C subdir

In my sub Makefile, I used this kind of rules:

...
%.o : %.cc
        $(CXX) -c  $< -o $@ $(CPPFLAGS) 
...

I failed to get "-g" to my sub Makefile. Could you point out what might help? 
Or what can be an alternative solution?

I've used cygwin and my make is

GNU Make 3.80
Copyright (C) 2002  Free Software Foundation, Inc.
This is free software; see the source for copying conditions.
There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A
PARTICULAR PURPOSE.

Br,

- Chenfu