sys/resource.h: add PRIO_MIN and PRIO_MAX for getpriority and setpriority
sys/resource.h: add PRIO_MIN and PRIO_MAX for getpriority and setpriority

These constants are not specified by POSIX, but they are in the reserved
namespace, glibc and bsd systems seem to provide them as well.
(Note that POSIX specifies -NZERO and NZERO-1 to be the limits, but
PRIO_MAX equals NZERO)

chardi/musl,chardi/musl,chardi/musl