[clang] [llvm] [ARM] Armv8-R does not require fp64 or neon. (PR #88287)

[Chris Copeland via cfe-commits]

chrisnc wrote:

Understood. FWIW, `arm-none-eabi-gcc` does not enable any FPU features by default with `-march=armv8-r` (and will error out if you combine that with `-mfloat-abi=hard`), which is what the first pass of this PR went for, but I think where we landed is a decent middle ground.

https://github.com/llvm/llvm-project/pull/88287