[llvm] [aarch64][win] Add support for import call optimization (equivalent to MSVC /d2ImportCallOptimization) (PR #121516)

[Daniel Paoliello via llvm-commits]

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@@ -77,6 +78,11 @@ static cl::opt<PtrauthCheckMode> PtrauthAuthChecks(
     cl::desc("Check pointer authentication auth/resign failures"),
     cl::init(Default));
 
+static cl::opt<bool> EnableImportCallOptimization(
+    "aarch64-win-import-call-optimization", cl::Hidden,
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dpaoliello wrote:

I can do a follow-up PR to switch this to a function attribute (again, it'll make x64 easier since I'll probably have to disable some optimizations to get it to work).
My only question with that is: is there a way to mark all functions with an attribute without having to add an option to the frontend? Or am I going to have to flow this through to Clang?

https://github.com/llvm/llvm-project/pull/121516