util/time test fails on OpenBSD

The Pixelminers buildbot shows failures on the util/time test, see https://buildbot.pixelminers.net/builders/OpenBSD/builds/970/steps/shell_3/logs/stdio

util/time: 
  FAIL src/test/test_util.c:302: assert(LONG_MAX OP_EQ tv_udiff(&start, &end)): 2147483647 vs -6005000
  [time FAILED]