[Async CC] Auth'd AFP ptr of statically thin fn.

In irgen::getAsyncFunctionAndSize, in the case where the passed-in
function has a thin representation, the pointer that is passed in is not
actually a pointer to a function but instead a pointer to an
AsyncFunctionPointer struct.  To obtain the function pointer and size,
fields must be loaded from this struct.  However, in order to load these
fields, that pointer to the AsyncFunctionPointer struct must itself
first be authenticated.  Here, that authentication is performed.
Subsequently, the function pointer is again signed.

Author: nate-chandler

lib/IRGen/GenCall.cpp

@@ -2039,6 +2039,9 @@ std::pair<llvm::Value *, llvm::Value *> irgen::getAsyncFunctionAndSize(
   case SILFunctionTypeRepresentation::Closure:
   case SILFunctionTypeRepresentation::Block: {
     auto *ptr = functionPointer.getRawPointer();
+    if (auto authInfo = functionPointer.getAuthInfo()) {
+      ptr = emitPointerAuthAuth(IGF, ptr, authInfo);
+    }
     auto *afpPtr =
         IGF.Builder.CreateBitCast(ptr, IGF.IGM.AsyncFunctionPointerPtrTy);
     llvm::Value *fn = nullptr;
@@ -2051,6 +2054,9 @@ std::pair<llvm::Value *, llvm::Value *> irgen::getAsyncFunctionAndSize(
             Address(addrPtr, IGF.IGM.getPointerAlignment()), /*isFar*/ false,
             /*expectedType*/ functionPointer.getFunctionType()->getPointerTo());
       }
+      if (auto authInfo = functionPointer.getAuthInfo()) {
+        fn = emitPointerAuthSign(IGF, fn, authInfo);
+      }
     }
     llvm::Value *size = nullptr;
     if (emitSize) {