[compiler-rt] [compiler-rt][ARM] Optimized mulsf3 and divsf3 (PR #168394)

[Simon Tatham via llvm-commits]

statham-arm wrote:

This PR is initially a sequence of four commits already. The first is #161546 unchanged; the next three fix build and test failures, two of which were found by buildbots after the previous attempt, and the third I found myself during re-testing. I know they'll all be squashed together into one commit for landing, but I keep them separate to make review easier.

https://github.com/llvm/llvm-project/pull/168394