Merge pull request #79727 from gottesmm/pr-025c1133954b74e7b4eda77e1a6f3bcafd4eb6cf

[concurrency] Add initial support for SwiftSettings to control defaultIsolation at the file level.

lib/Serialization/Serialization.cpp

@@ -5130,6 +5130,9 @@ public:
         case BuiltinMacroKind::IsolationMacro:
           builtinID = 2;
           break;
+        case BuiltinMacroKind::SwiftSettingsMacro:
+          builtinID = 3;
+          break;
         }
         break;
       }