[clang] [libclc] [llvm] [openmp] [Clang] `__attribute__((assume))` refactor (PR #84934)

[Sven van Haastregt via cfe-commits]

svenvh wrote:

The libclc usage seems to have been added by @rjodinchr in https://reviews.llvm.org/D147773 (and approved by @alan-baker).  Perhaps they have an opinion?

https://github.com/llvm/llvm-project/pull/84934