Prevent a compiler warning for an unused variable
Allow the Valgrind wrapper to use more than one core (even though it runs
really slow when emulating more than one worker thread, it is useful
to test those code paths once in a while)
Force the thread stacks to pre-fault their pages.

This fixes an issue with Fedora's default virtual memory settings where
there would be audio drop-outs after opening a big project until all of the
pages were faulted into memory.  (and also prevents this from happening
on other distros that I don't regularly test)