[llvm] [Offload] Prevent by default passing CMAKE_CXX_FLAGS to GPU build (PR #160881)

[Shilei Tian via llvm-commits]

shiltian wrote:

Based on my experience, many people do use this flag globally to pass compile flags, even for GPU targets, not to build LLVM though. I understand is not great and do support this change, but I think it might be better to document this.

https://github.com/llvm/llvm-project/pull/160881