adding to existing makefile variables

[Peschko, Edward]

hey all,

I'm surpised this is not a FAQ, but what I'm trying to do is to add to an 
existing makefile variable, ie:

make CFLAGS+=-g

Unfortunately, this doesn't seem to do what I intend, namely looking in the 
makefile and extracting the CFLAGS variable, and then appending '-g' to it.

Instead, it looks in the *environment* to find a CFLAGS. Which is pretty 
useless because most packages take their CFLAGS variable from a line in a make 
file.

How do you 'reach in and grab' a makefile variable, and then add to it? 

Ed