[llvm] [x86] Enable indirect tail calls with more arguments (PR #137643)

[Hans Wennborg via llvm-commits]

zmodem wrote:

Thanks for the poke and comments! I've updated the patch to apply on top of main.

Since `getGPRsForTailCall` was removed in http://github.com/llvm/llvm-project/pull/156880 I've rewritten `checkTCRetRegUsage()` to use the register classes directly. (Also renamed it to `checkTCRetEnoughRegs`). @arsenm does that look reasonable to you?

I think getting perfect test coverage for this is pretty hard, but it's better now at least.

https://github.com/llvm/llvm-project/pull/137643