[llvm] [Support] Resolve symlinks in `getMainExecutable()` on Windows (PR #76304)

[Mike Hommey via llvm-commits]

glandium wrote:

It's not really relevant, but it's in the Firefox build system, using `llvm-config --cxxflags` and `llvm-config --ldflags`, and it wouldn't handle the quoting `sys::printArg` adds, but it's entirely our problem. I'm sure there are plenty of other scripts using `llvm-config` and not handling quoting properly (and not handling spaces properly today).

https://github.com/llvm/llvm-project/pull/76304