Adding an option to configure?

[Chris Telting]

I am trying to modify the configure script for gcc.  I am trying to add 
an option that would instruct it not to build gcclib.

something like: configure --nogcclib

Then depending upon a coresponding internally defined variable it would 
include or skip building it.

It all appears to be a bit of a mess.  The autoconf m4 files are global 
so I don't wish to modify those.  How does one add an option like this?