Makes A Microsoft Layout CodeGen Test Explicit

This patch tests introduces a proper codegen test in place of the 
"codegen no longer crashes" test introduced in r193664. The test is also 
moved from layout to CodeGenCXX.

Differential Revision: http://llvm-reviews.chandlerc.com/D2174



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@194739 91177308-0d34-0410-b5e6-96231b3b80d8