[CommandLine] Don't allow unlimitted dashes for options. Part 1 or 5

Summary:
Prior to this patch, the CommandLine parser would strip an
unlimitted number of dashes from options.  This patch limits it to
two.

Reviewers: rnk

Reviewed By: rnk

Subscribers: hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D61229

llvm-svn: 359480