How to optimize compiling Krita if you are a developer

1) use threading 'make -jN install', where N is the number of cores of your CPU;

2) Rebuild in subdirectories, e.g. for your patch it is enough to do 'cd krita/ui; make -j8 install';

3) When you changes are trivial (no UI, moc or cmake changes), you can use 'make -jN install/fast' option, which is much faster since it skips numerous checks