swift234

[test] Tweak test to avoid issues.

Upstream Clang changed how redeclarations of tag decls in different modules
get handled. Unfortunately, the /redefinition/ case causes problems for
Swift's current importing logic. r31684 was an attempt to fix this, but
not a successful one -- it treats all declarations like definitions. For
now, just contrive the test in such a way that it skirts these issues.

rdar://problem/22548309

Swift SVN r31823