Update GCC, GMP, MPFR and MPC

GCC updated from 4.6.3 to 4.6.4
GMP updated from 5.1.0 to 5.1.3
MPFR updated from 3.1.1 to 3.1.2
MPC updated from 1.0.1 to 1.0.2

gcc-4.6.3-fix54638.patch and gcc-4.6.3-texinfofix.patch were safely
removed since they were backports from GCC 4.6.4.

These are all bug & regression fixes only releases. Updating to GCC 4.6.4 allows compiling GCC with newer versions of host GCC and texinfo without the need of patches. The main GCC patch was re-synced against 4.6.4 and the backported patches from 4.6.4 were removed.

Tested and built successfully.