regression test for _Concurrency module shadowing behavior

Author: kavon

test/Concurrency/Inputs/ShadowsConcur.swift

@@ -0,0 +1,5 @@
+
+public struct Task {
+  public var someProperty : String = "123"
+  public init() { }
+}

test/Concurrency/concurrency_module_shadowing.swift

@@ -0,0 +1,13 @@
+// RUN: %empty-directory(%t)
+// RUN: %target-swift-frontend -emit-module -emit-module-path %t/ShadowsConcur.swiftmodule -module-name ShadowsConcur %S/Inputs/ShadowsConcur.swift
+// RUN: %target-typecheck-verify-swift -I %t -enable-experimental-concurrency
+// REQUIRES: concurrency
+
+
+import ShadowsConcur
+
+func f(_ t : Task) -> Bool {
+  return t.someProperty == "123"
+}
+
+func g(_: _Concurrency.Task) {}