[GSoC] Add support for CC1 options.

Summary:
Add value completion support for options which are defined in
CC1Options.td, because we only handled options in Options.td.

Reviewers: ruiu, v.g.vassilev, teemperor

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D34558

llvm-svn: 306127