[Parse] Add an IRGen test for @_objcRuntimeName.

rdar://problem/46546165

Author: mikeash

test/IRGen/objc_runtime_name_attr.swift

@@ -0,0 +1,17 @@
+// RUN: %empty-directory(%t)
+// RUN: %target-swift-frontend %s -emit-ir | %FileCheck %s
+
+// REQUIRES: objc_interop
+
+//import Foundation
+
+class NormalEverydayClass {}
+// CHECK: @"$s22objc_runtime_name_attr19NormalEverydayClassCMm" = hidden global %objc_class
+// CHECK: @_DATA__TtC22objc_runtime_name_attr19NormalEverydayClass = private constant
+
+
+@_objcRuntimeName(RenamedClass)
+class ThisWillBeRenamed {}
+// CHECK: @"$s22objc_runtime_name_attr17ThisWillBeRenamedCMm" = hidden global %objc_class
+// CHECK: @_DATA_RenamedClass = private constant
+