Summary:
This change enables `cl::Grouping` for short options --
options with names of a single character. This is consistent with GNU
getopt behavior.
Reviewers: rnk, MaskRay
Reviewed By: MaskRay
Subscribers: thopre, cfe-commits, MaskRay, rupprecht, hiraditya, llvm-commits
Tags: #llvm, #clang
Differential Revision: https://reviews.llvm.org/D61270
llvm-svn: 359917