bitbake: runqueue: Sanity check BB_NUMBER_THREADS

Bitbake does really weird things with negative or zero numbers of threads
which is confusing to the user. Add a sanity check for this.

When you have code doing arithmetic on the values and a VM reconfigures
to only a single thread, negative numbers are easier than you'd think.

(Bitbake rev: 32166ac3c85ff3c04081580ae76bd63590d6ff3e)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/lib/bb/runqueue.py

@@ -1280,6 +1280,9 @@ class RunQueueExecute:
         if rq.fakeworkerpipe:
             rq.fakeworkerpipe.setrunqueueexec(self)
 
+        if self.number_tasks <= 0:
+             bb.fatal("Invalid BB_NUMBER_THREADS %s" % self.number_tasks)
+
     def runqueue_process_waitpid(self, task, status):
 
         # self.build_stamps[pid] may not exist when use shared work directory.