MS wide bitfield error check in Sema

cl.exe treats wide bitfields as an error. This patch causes them to be
an error if IsMsStruct is true, as it is in straight C.

Patch by Warren Hunt!

Reviewers: eli.friedman

Differential Revision: http://llvm-reviews.chandlerc.com/D1125

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@186536 91177308-0d34-0410-b5e6-96231b3b80d8