[clang] [flang] [lld] [lldb] [llvm] [mlir] [polly] [CMake] respect LLVMConfig.cmake's LLVM_DEFINITIONS in standalone builds (PR #138587)

[Martin Storsjö via cfe-commits]

mstorsjo wrote:

> I rebased this on top of #138783 and adjusted the title and description. Now it should be in a good state to push cmake changes for other projects.

The changes look good, but it looks like the changes from #138783 still show up when viewing the changes; can you check that you've rebased past the merged #138783?

(Also, I take it that no other subprojects than clang need the `cmake_push_check_state` change?)

https://github.com/llvm/llvm-project/pull/138587