How to add a debug flag while compiling the kernel

Hi all,

I tried adding the -DDEBUG flag in the top level make file
but I get this error when I do "make bzImage"

In file included from init/do_mounts.c:913:
init/../lib/inflate.c: In function `inflate':
init/../lib/inflate.c:999: warning: implicit declaration of function `fprintf'
init/../lib/inflate.c:999: `stderr' undeclared (first use in this function)
init/../lib/inflate.c:999: (Each undeclared identifier is reported only once
init/../lib/inflate.c:999: for each function it appears in.)
make: *** [init/do_mounts.o] Error 1                          


How do I set the Debug flag while compiling the linux kernel.

Also I wonder if I have to edit the toplevel Makefile
can I do it using "make menuconfig" .Please let me know


Thanks