In upcoming changes, 'struct td_sched' will store CPU ID of the thread's
current runqueue instead of a pointer to the runqueue. This requires
functions to store pointer to the runqueue as a local variable. Although
the name 'runq' seams ideal for these local variables, it is already
taken by the global runqueue. Thus rename the global runqueue to
'runq_global' to hint the variable is the global runqueue and yield the
name 'runq' to local variables.
Suggested by: olce