msys2-runtime reports wrong commit hash in uname -r

[jeremyd2019]

the commit hash in uname -r output is the hash corresponding to the cygwin tag the msys2-runtime release is based on, not the commit hash of the msys2-runtime commit.

Git for Windows deals with this by recording the commit in update-patches.sh and passing that recorded commit into configure --with-msys2-runtime-commit.

Noticed while trying to track down a performance regression in curl/curl#16217 (comment).

[jeremyd2019]

I would have done a PR right then, but it didn't seem worth updating the msys2-runtime package just for that, so I entered an issue instead so hopefully we can remember to do that when updating msys2-runtime next time.