I'm not a mac user so my help may be limited in use (locate probably didn't work because updatedb needs to be run to update the file database).
but since you know where it is...
do
if it doesn't show anything then it's not had a symbolic link added and you can create one with
if it is there, make sure the path is correct.
I think
but since you know where it is...
do
ls -l /usr/bin/gcc
if it doesn't show anything then it's not had a symbolic link added and you can create one with
ln -s /path/to/real/gcc /usr/bin/gcc
if it is there, make sure the path is correct.
I think
ls -alwill show you the symbolic link and it's target