This change refactors the existing create_thread() function to be more
generic. It replaces almost all of its arguments by a callback that can
be used to extract the thread ID and copy it out to the right place, but
also to perform additional initialization steps, such as setting the
trapframe. This also makes the difference between thr_new() and
thr_create() more clear in my opinion.
This function is going to be used by the CloudABI compatibility layer.
Reviewed by: kib
MFC after: 1 month
82a3d2cbfc