Revert commit c90c7a33f53ad88dfcc583ad4c77bec306da0b22
targets.mk: Revert to cleanup at every compile for 'standard' targets.
Note: You can do 'dirty' builds with 'make compile-dirty' and 'make
test-dirty'.
- Disadvantage: these builds may fail due to the missing clean.
- Advantage: typically the 'dirty' builds are much faster.