[clang] [Clang][Unittest] Support for `target` update directive and `from` clause in clang unittests (PR #150580)

[Amit Tiwari via cfe-commits]

amitamd7 wrote:

Added here `update to` clause changes too as creating separate PR for this won't make much sense.

https://github.com/llvm/llvm-project/pull/150580