Adjust to addition of llvm::Attribute::SwiftAsync

This the Swift change to go with the llvm PR
swiftlang/llvm-project#2274.

Author: aschwaighofer

lib/IRGen/GenCall.cpp

@@ -487,6 +487,14 @@ static void addIndirectResultAttributes(IRGenModule &IGM,
                               b);
 }
 
+void IRGenModule::addSwiftAsyncContextAttributes(llvm::AttributeList &attrs,
+                                                 unsigned argIndex) {
+  llvm::AttrBuilder b;
+  b.addAttribute(llvm::Attribute::SwiftAsync);
+  attrs = attrs.addAttributes(this->getLLVMContext(),
+                              argIndex + llvm::AttributeList::FirstArgIndex, b);
+}
+
 void IRGenModule::addSwiftSelfAttributes(llvm::AttributeList &attrs,
                                          unsigned argIndex) {
   llvm::AttrBuilder b;
@@ -1515,6 +1523,9 @@ void SignatureExpansion::expandExternalSignatureTypes() {
       switch (FI.getExtParameterInfo(i).getABI()) {
       case clang::ParameterABI::Ordinary:
         break;
+      case clang::ParameterABI::SwiftAsyncContext:
+        IGM.addSwiftAsyncContextAttributes(Attrs, getCurParamIndex());
+        break;
       case clang::ParameterABI::SwiftContext:
         IGM.addSwiftSelfAttributes(Attrs, getCurParamIndex());
         break;

lib/IRGen/IRGenModule.h

@@ -1620,6 +1620,9 @@ private:                            \
   /// Add the swiftself attribute.
   void addSwiftSelfAttributes(llvm::AttributeList &attrs, unsigned argIndex);
 
+  void addSwiftAsyncContextAttributes(llvm::AttributeList &attrs,
+                                      unsigned argIndex);
+
   /// Add the swifterror attribute.
   void addSwiftErrorAttributes(llvm::AttributeList &attrs, unsigned argIndex);