[clang] [clang] [ARM] Explicitly enable NEON for Windows/Darwin targets (PR #122095)

[Martin Storsjö via cfe-commits]

mstorsjo wrote:

> Setting default features for a platform based on what we happened to choose (likely with a very thin justification) to be the default CPU sounds fragile to me, so I think this patch is a good step forward. Even if there weren't this downstream patch interacting with it, I think it would be a good change to make.

Indeed. And it follows in the same style as d0fbef9c753a78aa20d5a462b682bfaf83cc6e6e, which I in retrospect feel would have had very little tangible effect. CC @DanAlbert for that one, to potentially fill in more details about the reasoning around it.

https://github.com/llvm/llvm-project/pull/122095