add Copyable to a few -parse-stdlib tests

Since these tests may in the future have
a move-only type in it. If you're using
`-parse-stdlib -module-name Swift`
it's a good add Copyable, but not required,
at this time.

Author: kavon

test/SILGen/unmanaged_ownership.swift

@@ -1,6 +1,8 @@
 
 // RUN: %target-swift-emit-silgen -parse-stdlib -module-name Swift %s | %FileCheck %s
 
+@_marker protocol _Copyable {}
+
 class C {}
 
 enum Optional<T> {

test/SILOptimizer/nonescaping_partial_apply_gauntlet.swift

@@ -5,6 +5,7 @@
 // RUN: %target-swift-frontend -emit-sil -parse-stdlib -module-name Swift %s
 // RUN: %target-swift-frontend -emit-sil -O -parse-stdlib -module-name Swift %s
 
+@_marker protocol _Copyable {}
 precedencegroup CastingPrecedence {}
 precedencegroup AssignmentPrecedence {}