This adds -include_paths which can be a colon-separated list of paths that are searched for includes.
The semantics are:
include paths should be allowed as relative or absolute
include paths are searched first, in the order they are specified on the command line
if the included file is not found on any include path, fallback to searching from the working directory (which is the only place currently searched before this diff)
This adds -include_paths which can be a colon-separated list of paths that are searched for includes.
The semantics are: