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

[Oliver Hunt via cfe-commits]

================
@@ -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) {
----------------
ojhunt wrote:

Righto, I'll use string literals for now (and will move it to the macho place)

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