[llvm] [Windows] Avoid loading shared system libraries from user directory (PR #90520)

[Daniel Paoliello via llvm-commits]

https://github.com/dpaoliello approved this pull request.

Just to be clear, this means that we will never load the version of Dbghelp.dll that ships with the [Debugging Tools for Windows](https://learn.microsoft.com/en-us/windows/win32/debug/dbghelp-versions). I don't think that it will be an issue for `MiniDumpWriteDump`, so I'm approving this.

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