[clang] [llvm] [AArch64][llvm] Add support for Permission Overlays Extension 2 (FEAT_S1POE2) (PR #164912)

[Jonathan Thackray via llvm-commits]

================
@@ -814,10 +814,12 @@ def lookupBTIByName : SearchIndex {
   let Key = ["Name"];
 }
 
+def : BTI<"r",  0b000>;
----------------
jthackray wrote:

Page 118 of the POE2 `00eac1` specification:
```
If FEAT_BTIE is implemented, then encoding 00 when executed from an Enhanced Guarded Page is allocated as target “r”.
```

https://github.com/llvm/llvm-project/pull/164912