Issue #12871: sched_get_priority_(min|max) might not be defined even though
<sched.h> is available (most notably on OpenBSD when built without pthread):
add an explicit configure check.
diff --git a/configure.in b/configure.in
index 43745fb..5b0f11e 100644
--- a/configure.in
+++ b/configure.in
@@ -2538,7 +2538,8 @@
select sem_open sem_timedwait sem_getvalue sem_unlink sendfile setegid seteuid \
setgid sethostname \
setlocale setregid setreuid setresuid setresgid setsid setpgid setpgrp setpriority setuid setvbuf \
- sched_setaffinity sched_setscheduler sched_setparam sched_rr_get_interval \
+ sched_get_priority_max sched_setaffinity sched_setscheduler sched_setparam \
+ sched_rr_get_interval \
sigaction sigaltstack siginterrupt sigpending sigrelse \
sigtimedwait sigwait sigwaitinfo snprintf strftime strlcpy symlinkat sync \
sysconf tcgetpgrp tcsetpgrp tempnam timegm times tmpfile tmpnam tmpnam_r \