[clang-tidy] Add -extra-arg and -extra-arg-before to run-clang-tidy.py
[clang-tidy] Add -extra-arg and -extra-arg-before to run-clang-tidy.py

Summary:
These flags allow specifying extra arguments to the tool's command
line which don't appear in the compilation database.

Reviewers: alexfh

Differential Revision: https://reviews.llvm.org/D28334

git-svn-id: a34e9779ed74578ad5922b3306b3d80a0c825546@292415 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/clang-tools-extra,llvm-mirror/clang-tools-extra,llvm-mirror/clang-tools-extra,llvm-mirror/clang-tools-extra