[clang] [clang] Enable --print-supported-extensions for all targets (PR #66586)

[David Spickett via cfe-commits]

DavidSpickett wrote:

Thankyou for looking into this, if it can work it's much cleaner than an ever expanding if.

I think that `getAllProcessorFeatures` my include things that are rejected by `-march`. I will check that for Arm and AArch64. Since the list of features in the target parser may be different than the backend (it's not good but it is what it is).

Does this change RISC-V's output? They are (I assume) unique in printing version numbers and ratification status, etc. Assuming it doesn't (which it probably does), it would likely make a few methods in RSIC-V ABI info unused, but deal with that later if so.

https://github.com/llvm/llvm-project/pull/66586