Update GCC and binutils

Toolchain updates:
 - sys-devel/gcc-4.8.3
 - sys-devel/binutils-2.24-r3
 - sys-devel/flex-2.5.39-r1
 - dev-libs/gmp-5.1.3-r1
 - dev-libs/mpc-1.0.1
 - dev-libs/mpfr-3.1.2-r1
( + other misc dependencies )

Currently waiting on some test builds to make sure nothing dramatic happens.