[Openmp-commits] [openmp] [openmp] On Windows, fix standalone cmake build (PR #80174)

[Shilei Tian via Openmp-commits]

shiltian wrote:

`append_if(TRUE...)` looks like a "hack" to me. Can we add the def of `append` and implement `append_if` with that?

https://github.com/llvm/llvm-project/pull/80174