- make should be $(MAKE)
- add + in front of rules spawning long-lasted make process in a
subshell. (This would not be needed with $(MAKE) -C .. target, but our
makefiles do not handle that because they use $(PWD))
- split the main 'all' rule as all 4 targets are independant
- fix dependencies where appropriate for parallelism
Extra, not speed-related changes:
- remove some double-colon for targets as they do not need it
This cuts build time from 5s to 1.5s on a laptop with -j4, and more
importantly from 85s to 35s on a KNL node.
As a bonus, the fixed dependencies removes the need to clean before
rebuilding all the time. Probably.
