[llvm] [Cygwin] Fix global variable dll import (PR #121439)

[Mateusz Mikuła via llvm-commits]

mati865 wrote:

I can look into it, but probably not sooner than mid-January. My initial plan was to keep the changes as patches for MSYS2 and, after confirming they work, upstream them.

https://github.com/llvm/llvm-project/pull/121439