Recover from errors in enum definition

Previously any error in enum definition body stopped parsing it. With this
change parser tries to recover from errors.
The patch fixes PR10982.

Differential Revision: http://llvm-reviews.chandlerc.com/D2018


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@198259 91177308-0d34-0410-b5e6-96231b3b80d8