Add a few dllimport/dllexport tests. NFC

Summary:
This change just adds tests for some corner cases of dllimport/dllexport,
primarily for some static methods.

We plan to enable dllimport/dllexport support for the PS4, and these
additional tests are for points we previously were testing internally.

-Warren Ristow
SN Systems - Sony Computer Entertainment Group

Reviewers: rnk

Subscribers: silvas

Differential Revision: http://reviews.llvm.org/D17775

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@262442 91177308-0d34-0410-b5e6-96231b3b80d8