If you want to install it as a local user
GNU GSRC provides an easy way to do so
Link: http://www.gnu.org/software/gsrc/
After configuration, simply specify the following commands:
cd gsrc
make -C pkg/gnu/gcc
make -C pkg/gnu/gcc install
The second step could also be changed to speed up for an N-core system:
make -C pkg/gnu/gcc MAKE_ARGS_PARALLEL="-jN"