Summary:
Xcode's compilation databases follows a different convention than cmake's and
escape the `"file"` and `"dir"` fields of each unit to make them shell-ready.
We need to treat them differently when reading them.
This adds a new `--clang-compilation-db-files-escaped` option and makes the
code related to reading compilation databases deal correctly with both
conventions.
Reviewed By: akotulski
Differential Revision: D4559239
fbshipit-source-id: 51120ae
Jules Villard