Really just for convenience so the developer can choose appropriate
values for CMake options PARALLEL_COMPILE_JOBS and PARALLEL_LINK_JOBS.
Might also help to find out why builds are slow.
* Fix includes
* Faster compile
* WTFix
* Limit compile and linking jobs according to available memory
* Add comment
* fix
* Remove ALL from copy-headers target
* Freebsd fix
* Better
* cmake: split use libcxx