Installing GCC & MSYS2

pacman -S --needed base-devel mingw-w64-i686-toolchain mingw-w64-x86_64-toolchain git subversion mercurial mingw-w64-i686-cmake mingw-w64-x86_64-cmake

Add C:\msys64\mingw64\bin and C:\msys64\mingw32\bin, in that order, to your PATH

add

C:\msys64\usr\bin
if needed

edit C:\msys64\msys2.ini

MSYS2_PATH_TYPE=inherit

References
https://github.com/orlp/dev-on-windows/wiki/Installing-GCC–&-MSYS2