[Clang][AArch64] Emit 'unimplemented' diagnostic for SME#80295

sdesmalen-arm merged 2 commits intollvm:mainllvm/llvm-project:mainfrom

sdesmalen-arm:sme-clang-unimplemented-za-spill-restore-diagnosticsdesmalen-arm/llvm-project:sme-clang-unimplemented-za-spill-restore-diagnosticCopy head branch name to clipboard