Improve operator kind detection in presence of comments.

We used to incorrectly identify some operators (*, &, +, -, etc.) if
there were comments around them.

Example:
Before: int a = /**/ - 1;
After:  int a = /**/ -1;

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@172533 91177308-0d34-0410-b5e6-96231b3b80d8