cmake: Add `clint` target to build Makefile
Allows linting only modified files and linting multiple files in parallel. In the current state is rather slow because errors.json is a 6 MiB file and needs to be reparsed each time. Results on my system (6-core): # In build dir, actually parallel make -j5 clint 241.24s user 8.39s system 334% cpu 1:14.74 total # In root, one process make -j5 clint 60.69s user 0.37s system 93% cpu 1:05.19 total In both cases download time included. That is not well for travis (though I would keep travis as-is because new variant will fail before checking all files), but already good enough for regular development: total times are nearly identical and this is the *full* build, further `make -C build clint` will check only modified files.
Showing with 93 additions and 55 deletions