[coreboot] Updated coreboot build environment for Windows

[Scott Duplichan]

I have maintained a coreboot build environment for Windows for a while:
http://notabs.org/coreboot/windows-build.htm

Though maintaining it has never been a priority for me,
the website log files show quite a few people download it.
For this reason I am trying to improve this project. The 
recently submitted patches get the Windows hosted coreboot
build environment working well enough for abuild to pass
for all builds using gcc: x86, ARM, and AARCH64. There is
no clang or riscv support.

There is one patch I haven't been able to submit. For Windows
hosted building, file util/nvidia/cbootimage/src/set.c needs
to fopen binary files using "rb" instead of "r". This file
is part of a git 'submodule'. How do build and upload a patch
for this file?

Thanks,
Scott