[llvm] [Windows] Use absolute path when loading system shared library (PR #90520)

[via llvm-commits]

jofrn wrote:

Your comments are valuable. Ensuring it can cross-compile through this route may be tricky; it looks like it is feasible to modify the search path of LoadLibraryW directly, so that may prove to be a better solution.

https://github.com/llvm/llvm-project/pull/90520