Fix diagnostics when @warn_unused_result is used with other attrs

Author: tanadeau

lib/Parse/ParseDecl.cpp

@@ -1358,7 +1358,7 @@ bool Parser::parseDeclAttribute(DeclAttributes &Attributes, SourceLoc AtLoc) {
       diagnose(AtLoc, diag::attr_warn_unused_result_removed)
         .fixItRemove(SourceRange(AtLoc, attrLoc));
 
-      return true;
+      return false;
     }
 
     // @warn_unused_result with arguments.
@@ -1379,7 +1379,7 @@ bool Parser::parseDeclAttribute(DeclAttributes &Attributes, SourceLoc AtLoc) {
     diagnose(AtLoc, diag::attr_warn_unused_result_removed)
       .fixItRemove(SourceRange(AtLoc, rParenLoc));
 
-    return true;
+    return false;
   }
 
   if (DK != DAK_Count && !DeclAttribute::shouldBeRejectedByParser(DK))

test/attr/attr_discardableResult.swift

@@ -104,3 +104,9 @@ func f(a : () -> Int) {
 }
 
 @warn_unused_result func g() -> Int { } // expected-warning {{'warn_unused_result' attribute behavior is now the default}} {{1-21=}}
+
+class X {
+  @warn_unused_result // expected-warning {{'warn_unused_result' attribute behavior is now the default}} {{3-23=}}
+  @objc
+  func h() -> Int { }
+}