trunk 20191205 ftbfs on the Hurd, i686-gnu:

./../../src/libgo/go/runtime/os_hurd.go:42:7: error: reference to undefined field or method 'mos'
   42 |  if mp.mos.waitsema != 0 {
      |       ^
../../../src/libgo/go/runtime/os_hurd.go:55:4: error: reference to undefined field or method 'mos'
   55 |  mp.mos.waitsema = uintptr(unsafe.Pointer(sem))
      |    ^
../../../src/libgo/go/runtime/os_hurd.go:65:48: error: reference to undefined field or method 'mos'
   65 |   if sem_timedwait((*_sem_t)(unsafe.Pointer(_m_.mos.waitsema)), &ts) != 0 {
      |                                                ^
../../../src/libgo/go/runtime/os_hurd.go:75:46: error: reference to undefined field or method 'mos'
   75 |   r1 := sem_wait((*_sem_t)(unsafe.Pointer(_m_.mos.waitsema)))
      |                                              ^
../../../src/libgo/go/runtime/os_hurd.go:89:41: error: reference to undefined field or method 'mos'
   89 |  if sem_post((*_sem_t)(unsafe.Pointer(mp.mos.waitsema))) != 0 {
      |                                         ^
../../../src/libgo/go/runtime/os_hurd.go:95:21: error: reference to undefined name '_SC_NPROCESSORS_ONLN'
   95 |  n := int32(sysconf(_SC_NPROCESSORS_ONLN))
      |                     ^
Makefile:2836: recipe for target 'runtime.lo' failed
make[6]: *** [runtime.lo] Error 1