Mark as jobs unsafe, the port doesn't build in parallel.

% for i in jot 20; do { make clean && make; } >/dev/null 2>&1; echo -n " $?"; done; echo
0 0 0 0 0 0 1 0 0 1 0 0 0 0 0 1 1 0 0 0
% for i in jot 20; do { make clean && make -DMAKE_JOBS_UNSAFE; } >/dev/null 2>&1; echo -n " $?"; done; echo
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0