Changed to compile by forking() off subprocesses. On a six-core box this cuts wallclock time for make compiler from two and a half minutes to one and a half minutes. This can be disabled by setting compile_in_subprocesses to FALSE in src/lib/compiler/toplevel/main/compiler-controls.pkg or doing
eval: set_control "compiler::compile_in_subprocesses" "FALSE";
at the Mythryl interactive prompt.