Merge pull request #27479 from varungandhi-apple/vg-track-clang-function-types

Track Clang function types in the AST

include/swift/Basic/LangOptions.h

@@ -219,6 +219,13 @@ namespace swift {
     /// Build the ASTScope tree lazily
     bool LazyASTScopes = true;
 
+    /// Use Clang function types for computing canonical types.
+    /// If this option is false, the clang function types will still be computed
+    /// but will not be used for checking type equality.
+    /// FIXME: [clang-function-type-serialization] This option should be turned
+    /// on once we start serializing clang function types.
+    bool UseClangFunctionTypes = false;
+
     /// Whether to use the import as member inference system
     ///
     /// When importing a global, try to infer whether we can import it as a