[llvm] [AArch64] Switch to soft promoting half types. (PR #80576)

[Harald van Dijk via llvm-commits]

hvdijk wrote:

> Ah sorry, my bad! I'm not sure why I thought it was an ABI break. Looking at how your patch changes the tests I see now it doesn't look like it. However, is this something still worth mentioning in release notes somewhere?

Possibly, yes. Ideally I would like to get multiple arches moved over (ARM already done, a few other ones I'll be able to submit PRs for next week), so maybe it should be in the general release notes with a list of affected arches? AArch64 is probably the one it will have the least impact on: the default configuration is unaffected because it supports FP16 natively. Not sure what's best here, I would welcome some input.

https://github.com/llvm/llvm-project/pull/80576