add negative test for invalid references and declaration emit

tests/baselines/reference/declarationEmit_invalidReference2.errors.txt

@@ -0,0 +1,5 @@
+==== tests/cases/compiler/declarationEmit_invalidReference2.ts (1 errors) ====
+    /// <reference path="invalid.ts" />
+    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+!!! File 'invalid.ts' not found.
+    var x = 0;

tests/cases/compiler/declarationEmit_invalidReference2.ts

@@ -0,0 +1,3 @@
+// @declaration: true
+/// <reference path="invalid.ts" />
+var x = 0;