[clang] [clang] Reject character devices in #embed for now (PR #135370)

[Aaron Ballman via cfe-commits]

https://github.com/AaronBallman commented:

I think we should add some test coverage for both Windows and Linux. I think on Linux we can use `/dev/urandom` and on Windows we could use something like `COM1` on Windows. WDYT?

Also, these changes should come with a release note.

https://github.com/llvm/llvm-project/pull/135370