[compiler-rt] [Compiler-rt] Add AArch64 routines for __arm_agnostic("sme_za_state") (PR #120059)

[Kerry McLaughlin via llvm-commits]

================
@@ -204,6 +206,161 @@ DEFINE_COMPILERRT_FUNCTION(__arm_get_current_vg)
   ret
 END_COMPILERRT_FUNCTION(__arm_get_current_vg)
 
+DEFINE_COMPILERRT_FUNCTION(__arm_sme_state_size)
+  .variant_pcs __arm_sme_state_size
+  BTI_C
+
+  // Test if SME is available and PSTATE = 1.
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kmclaughlin-arm wrote:

```suggestion
  // Test if SME is available and PSTATE.ZA = 1.
```

https://github.com/llvm/llvm-project/pull/120059