Start by narrowing the problem down. Is it specific to Linux, or does it happen with gcc on other systems? Is it specific to the kernel version? Library version? Does it go away if you link static? Can you trim the program down to something short that demonstrates the bug?
Having done that, you'll know what program(s) the bug is in. For
GCC, the bug reporting procedure is explained in the info file. For
ld.so or the C or maths libraries, send mail to
firstname.lastname@example.org. If possible, include a short and
self-contained program that exhibits the bug, and a description both
of what you want it to do, and what it actually does.
If you want to help with the development effort for GCC or the C
library, the first thing to do is join the
email@example.com mailing list. If you just want to see
what the discussion is about, there are list archives at
http://homer.ncm.com/linux-gcc/. The second and subsequent
things depend on what you want to do!