[llvm] [OpenMP] Remove dependency on LLVM include directory from DeviceRTL (PR #136359)

[Joseph Huber via llvm-commits]

jhuber6 wrote:

> > but there's no reason to make `openmp/` depend on LLVM headers just for a single constant `1` value.
> 
> There is definitely a reason, and that's to avoid hardcoding things.
> 
> There are precedents where definitions of certain enumerations are duplicated. You could follow that---copy/paste the definition of the one that's introducing the dependence with a comment that it must be in sync with the one in LLVM.

Updated, better?

https://github.com/llvm/llvm-project/pull/136359