Add regression test

ahejlsberg · ahejlsberg · commit 2f4c8ebf1355 · 2017-12-19T19:58:28.000-08:00
diff --git a/tests/cases/compiler/unionSignaturesWithThisParameter.ts b/tests/cases/compiler/unionSignaturesWithThisParameter.ts
@@ -0,0 +1,13 @@
+// @strict: true
+
+// Repro from #20802
+
+function x<T>(ctor: {
+    (this: {}, v: T): void;
+    new(v: T): void;
+} | {
+    (v: T): void;
+    new(v: T): void;
+}, t: T) {
+    new ctor(t);
+}
