Building system libs with debugging symbols

[Micah]

The gnome maintainers need me to rebuild libpthread and libc with 
debugging symbols in order to get a more complete stack trace of a 
firefox crash. How exactly do I go about doing that, since those libs 
are part of world? Do I have to rebuild world or can I just rebuild 
those libs? What mods to make.conf or environmental variables do I need 
to set?


Thanks,
Micah