For better robustness, the Makefile emitter should be rewritten.

Depenencies between modules should be emitted (to be safe against
parallel make, and to be safe when one .pm file changes).

The reason is that rakudo only loads .pir files
if the timestamp is larger or equal to that of the .pm/.pm6 file. And when a
not-precompiled version of a module is loaded, precompilation of all
subsequent .pm files can cause weird errors in Rakudo.
