[llvm] [X86] Support EGPR (R16-R31) for APX (PR #70958)

[Nikita Popov via llvm-commits]

nikic wrote:

After https://github.com/llvm/llvm-project/pull/71797 the compile-time results look like this: https://llvm-compile-time-tracker.com/compare.php?from=f67158422c3bf37ce3884f4579a93f65e083e7fa&to=e05b18a8f2f2e0518c59a617c59daedb81adc212&stat=instructions:u

The `O0` regressions are pretty minimal now, so I think this is good enough to go ahead.

https://github.com/llvm/llvm-project/pull/70958