I think the best source for these information is searching
and possiply joining the gcc mailing list and ask there:
The project home page is http://gcc.gnu.org/
I'm afraid I didn't find a statement about the error message format
at the special gcc 3.0 page.
And be very very careful when you like to experiment with installing
intermediate releases of parts the system bases on (kernel, kernel compiler
libc and binutils), I distroyed some linux installations in the phase from
gcc 2.7.2 to 2.95 ...