Add IR and codegen support for deactivation symbols.
Deactivation symbols are a mechanism for allowing object files to disable
specific instructions in other object files at link time. The initial use
case is for pointer field protection.
For more information, see the RFC:
https://discourse.llvm.org/t/rfc-deactivation-symbols/85556
Reviewers: ojhunt, nikic, fmayer, arsenm, ahmedbougacha
Reviewed By: fmayer
Pull Request: https://github.com/llvm/llvm-project/pull/133536
