Running 'make' in the subfolder' where you got 'vfork' errors should update the library with the missing pieces - so you shouldn't have to do any more 're-make final library' stuff.
After "make" in the concerned subfolder I came back to the root folder and issued "make test". But errors were reported during the tests so I thought the library had not been finalized.
Alternative way of achieving incremental build is the following command in the top-level dir. [But this can also take a while to complete]
make ACTION=lib tree
BTW: do you have an antivirus or some type of scanner software thats running? Would disabling such a thing make the "vfork: Resource temporarily unavailable" problem go away?
Thanks for the hints. Yes I have a virus scanner and I believe I once disabled it for a test and it did not help, but am not absolutely certain any more. Will try next time the problem occurs. Regards, Dominik