-# - parallel - number of parallel process to be spawned for building
-# sources. Parallel building needs to be supported by the
-# underlying build system for this option to be effective.
-# Defaults to undef (i.e. parallel disabled, but do not try to
-# enforce this limit by messing with environment).
+# - parallel - max number of parallel processes to be spawned for building
+# sources (-1 = unlimited; 1 = no parallel)