[clang] [clang][PAC][darwin] Set correct default ptrauth features for arm64e-darwin (PR #153722)

[Ahmed Bougacha via cfe-commits]

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@@ -3291,6 +3291,39 @@ void Darwin::addClangTargetOptions(
     if (!RequiresSubdirectorySearch)
       CC1Args.push_back("-fno-modulemap-allow-subdirectory-search");
   }
+
+  if (getTriple().isArm64e()) {
+    auto EnsureDefaultPtrauthFlag = [&](OptSpecifier Pos, OptSpecifier Neg) {
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ahmedbougacha wrote:

Hmm, why not the more idiomatic `hasFlag`/`hasArg` and `push_back`?

https://github.com/llvm/llvm-project/pull/153722