[tests] improve the parse-stdlib test

Author: kavon

test/Sema/copyable_constraint.swift

@@ -0,0 +1,15 @@
+
+// >> First verify that when building the stdlib, we do have the copyable constraint. Note the module-name!!
+// RUN: not %target-swift-frontend -typecheck -parse-stdlib -module-name Swift %s 2>&1 | %FileCheck --check-prefix CHECK-SWIFT-MODULE %s
+
+// Now demonstrate that plain -parse-stdlib, such as in some arbitrary test, doesn't get the Copyable constraint.
+// But we also now can't declare a noncopyable type in this mode.
+// RUN: not %target-swift-frontend -typecheck -verify -parse-stdlib %s 2>&1 | %FileCheck %s
+
+@_marker public protocol Copyable {}
+
+func nextTime<T>(_ t: T) {}
+
+struct MO : ~Copyable {} // CHECK: cannot suppress implicit conformance to 'Copyable'
+
+nextTime(MO()) // CHECK-SWIFT-MODULE: move-only type 'MO' cannot be used with generics yet