[clang] [llvm] [AArch64] Add support for C1 CPUs (PR #171124)

[via llvm-commits]

dcandler wrote:

> It looks like all C1 series enabled SME and MOPS unconditionally. But according to Arm, only C1-Ultra/Premium are forced with SME support, and MOPS may cause performance degradation.

My understanding is that the convention of the `-mcpu` option is to enable all optional and mandatory features. The C1-Nano and Pro can be configured with SME, so the compiler should be able to support it, while MOPS is mandatory from v8.8.

https://github.com/llvm/llvm-project/pull/171124