[clang] [lldb] [llvm] [AArch64][TargetParser] autogen ArchExtKind enum - renaming (PR #90320)

[Jonathan Thackray via cfe-commits]

jthackray wrote:

> The command-line names or FEAT_ names should probably be what we are aiming for if we are changing them one-way or the other.

Yes, standardising on FEAT_* names would be good to match the TRM, so we avoid the
AEK_PREDRES/FEAT_SPECRES, AEK_PERFMON/FEAT_PMUv3, etc. mismatches.

https://github.com/llvm/llvm-project/pull/90320