Sadly, the majority of rakudo's and nqp's compilation is serialized (due
to the dependencies between the individual pieces).
If you build more than one backend at the same time, i.e. moar + jvm,
you can build both in parallel.
On the other hand, the biggest chunk of time is spent compiling the core
setting, which commonly takes a minute on moarvm.
nqp behaves very similarly.
moarvm on the other hand can compile all .c files at the same time and
use up as many cores as there are .c files, but it compiles so fast that
it's hardly worth anything.
hope that helps