[python] [tests] Fix test_linkage for unique external linkage
[python] [tests] Fix test_linkage for unique external linkage

Starting with r314037, anonymous namespaces no longer give
unique-external linkage to variables. However, this linkage can still be
achieved by using a type which is not exterally visible,
e.g. through being declared in an anonymous namespace but used outside
it. Fix the test to take advantage of that.

Differential Revision: https://reviews.llvm.org/D39810

git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@317986 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,llvm-mirror/clang,apple/swift-clang,apple/swift-clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,apple/swift-clang,apple/swift-clang,llvm-mirror/clang,llvm-mirror/clang,apple/swift-clang