[clang] [Clang][AArch64] Command-line options for A-profile's Sign Return Address Hardening (PR #176171)

[Anatoly Trosinenko via cfe-commits]

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@@ -3403,6 +3384,11 @@ def err_invalid_branch_protection_spec : Error<
   "invalid or misplaced branch protection specification '%0'">;
 def warn_unsupported_branch_protection_spec : Warning<
   "unsupported branch protection specification '%0'">, InGroup<BranchProtection>;
+def warn_attribute_harden_pac_ret_requires_pac_ret: Warning<
+  "'harden-pac-ret' attribute requires 'branch-protection=pac-ret'; 'target' attribute ignored">,
+  InGroup<IgnoredAttributes>;
+def err_invalid_harden_pac_ret_spec : Error<
+  "invalid or misplaced pac-ret hardening specification '%0'">;
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atrosinenko wrote:

[nit] At the only place I can see where `err_invalid_harden_pac_ret_spec` is reported, it is reported when `validateSignReturnAddressHardening` returns `std::nullopt`. Was "misspelled" intended instead of "misplaced"?

https://github.com/llvm/llvm-project/pull/176171