Refactor probe locking into shared functions

Refactor probe locking into shared functions

For scripts with thousands of probes, we save a fair amount of code-gen
time in pass-4 by having the common locking code extracted into shared
functions.

* runtime/probe_lock.h (stp_lock_probe, stp_unlock_probe): New.
* translate.cxx (c_unparser::emit_lock_decls): New, emits a static
  const array of locks needed for each probe.
  (c_unparser::emit_locks): Just call stp_lock_probe.
  (c_unparser::emit_unlocks): Just call stp_unlock_probe.