Auto merge of #2745 - vityafx:add-sched-constants-for-openbsd, r=Amanieu

Add SCHED constants for OpenBSD.

The constants are defined for improving the user experience when calling
the libc functions related to scheduling policies. Also helps with
unifiying the code as all these constants are already defined for other
operating systems.

libc-test/semver/openbsd.txt

@@ -708,6 +708,9 @@ RTLD_SELF
 RUSAGE_CHILDREN
 RUSAGE_SELF
 RUSAGE_THREAD
+SCHED_FIFO
+SCHED_OTHER
+SCHED_RR
 SCM_RIGHTS
 SCM_TIMESTAMP
 SEM_FAILED

src/unix/bsd/netbsdlike/openbsd/mod.rs

@@ -1165,6 +1165,10 @@ pub const _SC_NPROCESSORS_ONLN: ::c_int = 503;
 
 pub const FD_SETSIZE: usize = 1024;
 
+pub const SCHED_FIFO: ::c_int = 1;
+pub const SCHED_OTHER: ::c_int = 2;
+pub const SCHED_RR: ::c_int = 3;
+
 pub const ST_NOSUID: ::c_ulong = 2;
 
 pub const PTHREAD_MUTEX_INITIALIZER: pthread_mutex_t = 0 as *mut _;