[clang] [Clang] Deprecate `__is_trivially_relocatable` (PR #138835)

[via cfe-commits]

dyung wrote:

> LLVM Buildbot has detected a new failure on builder `llvm-clang-x86_64-sie-ubuntu-fast` running on `sie-linux-worker` while building `clang` at step 6 "test-build-unified-tree-check-all".
> 
> Full details are available at: https://lab.llvm.org/buildbot/#/builders/144/builds/24541
> 
> Here is the relevant piece of the build log for the reference

@cor3ntin can you take a look at this failure or revert to get the bot back to green?

https://github.com/llvm/llvm-project/pull/138835