[clang] [clang] Use the VFS to get the OpenMP entry info (PR #160935)

[Jan Svoboda via cfe-commits]

jansvoboda11 wrote:

Thanks for bringing this to my attention, @carlobertolli. I'm happy to take a look, but I'm unable to reproduce on macOS. Could you please create a self-contained LIT test independent of the host platform?

https://github.com/llvm/llvm-project/pull/160935