Enable test case for declaration emit for multiple file emit scenario

tests/baselines/reference/sourceMapWithMultipleFilesWithCopyright.js

@@ -31,4 +31,14 @@ Copyright
 ---------------------------------------------------------------------------*/
 ///<reference path="a.ts"/>
 var y = x;
-//# sourceMappingURL=a.js.map
+//# sourceMappingURL=a.js.map
+
+//// [a.d.ts]
+declare var x: {
+    a: number;
+    b: number;
+};
+declare var y: {
+    a: number;
+    b: number;
+};

tests/cases/compiler/sourceMapWithMultipleFilesWithCopyright.ts

@@ -1,5 +1,6 @@
 // @out: a.js
 // @sourcemap: true
+// @declaration: true
 // @Filename: a.ts
 /*--------------------------------------------------------------------------
 Copyright