The inclusion of mingw-w64-gcc for T5979.
This package contains gcc, g++, libraries, binaries, headers and
more software for building programs and projects targeting
MinGW-w64, 32 and 64 bits are supported but not multilib. The
MinGW-w64 Headers are added temporally here. Depends on
mingw-w64-binutils. Needs to be rebuilt again with modifications
in package.yml after rebuilding mingw-w64.

The build order is the following:
binutils -> headers -> bootstrap -> crt -> winpthreads -> gcc

Signed-off-by: Martin Reboredo <gc1000ll@gmail.com>

Built and tested (in Wine) a C "Hello, World!" program (with both GCC and Clang), a libstdc++ test, the godot export template, a simple Rust cross-compilation "Hello, World!" app and a Go cross-compiled sdl2 program (which also required a locally built SDL2 package).