Mark a couple of ReturnStmts implicit

These are both synthesized returns, so they ought
to be marked implicit.

Author: hamishknight

lib/Parse/ParseDecl.cpp

@@ -8733,7 +8733,7 @@ Parser::parseAbstractFunctionBodyImpl(AbstractFunctionDecl *AFD) {
         if (F->isFailable() && isa<NilLiteralExpr>(E)) {
           // If it's a nil literal, just insert return.  This is the only
           // legal thing to return.
-          auto RS = new (Context) ReturnStmt(E->getStartLoc(), E);
+          auto RS = new (Context) ReturnStmt(E->getStartLoc(), E, /*implicit*/ true);
           BS->setLastElement(RS);
           AFD->setHasSingleExpressionBody();
           AFD->setSingleExpressionBody(E);

lib/Sema/CodeSynthesis.cpp

@@ -1677,7 +1677,7 @@ static std::pair<BraceStmt *, bool>
 synthesizeSingleReturnFunctionBody(AbstractFunctionDecl *afd, void *) {
   ASTContext &ctx = afd->getASTContext();
   SmallVector<ASTNode, 1> stmts;
-  stmts.push_back(new (ctx) ReturnStmt(afd->getLoc(), nullptr));
+  stmts.push_back(new (ctx) ReturnStmt(afd->getLoc(), nullptr, /*implicit*/ true));
   return { BraceStmt::create(ctx, afd->getLoc(), stmts, afd->getLoc(), true),
            /*isTypeChecked=*/true };
 }