[clang] [llvm] [BPF] Add load-acquire and store-release instructions under -mcpu=v5 (PR #108636)

[Peilin Ye via cfe-commits]

peilin-ye wrote:

@eddyz87,

> Sorry for the delayed reply.

No worries at all!

> I'd say let's go with what you suggest, but avoid exit(1) call. We need to figure out how to do fail() w/o backtrace, but that is outside of the scope for this pull request.

Got it, rebased and added a 4th commit (can't say I like the one-commit-per-PR policy either :-) to do this in v3.  Please take another look.

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Also, just a heads-up: I think this PR is blocked by [an issue that I mentioned earlier on LKML](https://lore.kernel.org/all/ZujIlLqBEGOsxYRa@google.com/) (Cc: @4ast).  After that is resolved, I think we should change this PR to use `0x5` for the new mode modifiers (`BPF_MEMACQ`, `BPF_MEMREL`).

https://github.com/llvm/llvm-project/pull/108636