Correctly detect colon in bit fields. Fixes PR17333.

Summary: Colon was incorrectly detected as a start of inheritance list. Fixed.

Reviewers: djasper

Reviewed By: djasper

CC: cfe-commits, klimek

Differential Revision: http://llvm-reviews.chandlerc.com/D1884

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@192349 91177308-0d34-0410-b5e6-96231b3b80d8