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.
Merge pull request #44 from Bracket-/gcc-minor

Update GCC, GMP, MPFR and MPC