Wed, Feb 26, 2025, 06:35:33 PM GMT

Some `clangarm64` fixes (#5439)

Most notably, this fixes
https://github.com/git-for-windows/git/issues/5431, i.e. that the ARM64
flavor of Git for Windows does not use `/etc/gitconfig` by mistake, but
`/clangarm64/etc/gitconfig` instead.

My original intention was to fix only that issue, but when I fired up a
Git for Windows/ARM64 SDK and tried to build, I immediately ran into
trouble, then noticed places where ARM64 was not yet handled, and one
thing led to another and now it's a 6-patch PR instead of a single-patch
one.