[llvm] [WIP][Offload] Introduce ATTACH map-type support for pointer attachment. (PR #149036)

[via llvm-commits]

agozillon wrote:

Out of interest, will this change break any of the existing possible mappings clang used to emit (such as B and C in your examples in the description)? I ask as Flang's mappings are based on the way Clang currently handles its mapping, so if this breaks any pre-existing map behaviour, then there's a possibility it'll break a chunk of Flang OpenMP's offload capabilities. 

It's of course more than fine if it does, but would be good to know ahead of time if there's things that we'd need to address on the Flang side immediately or if we can more slowly phase in the attach system once this PR has landed :-)

There's a chunk of fortran OpenMP map tests in check-offload (not a comprehensive set, but it is a good cursory view on if anything might be broken by the changeset) that can be ran to help verify if things are reasonably okay.

As an unrelated side note, would be nice if we could align the mapping systems in Flang/Clang one day...

https://github.com/llvm/llvm-project/pull/149036