[clang-diff] Add commandline arguments.

Summary:
Support command line options for build path and extra arguments
This emulates the options accepted by clang tools that use CommonOptionsParser.

Add a flag for controlling the maximum size parameter for bottom up matching.

Reviewers: arphaman

Subscribers: klimek

Differential Revision: https://reviews.llvm.org/D36177

llvm-svn: 311173