GCC 4.7.4 toolchain Beta 6

Mingw64 GCC 32 bit toolchain using version 4.7.4 (git 4.7 branch with patches)

Install support packages before installing toolchain packages.

The gmp4 and extra support packages are needed to build support and toolchain packages.

The packages are for the MSys2 MINGW32 environment and are installed to /opt/mingw32 folder.