maybe openbsd has schedyield now

include/libc.h

diff --git a/include/libc.h b/include/libc.h
index 88382c1..ff7e7be 100644
--- a/include/libc.h
+++ b/include/libc.h
@@ -832,10 +832,6 @@
 #	endif
 #endif
 
-#ifdef __OpenBSD__
-#define sched_yield()	syscall(302)	/* what is this? */
-#endif
-
 /* command line */
 extern char	*argv0;
 extern void __fixargv0(void);

include/u.h

diff --git a/include/u.h b/include/u.h
index 1489ebd..68a08a6 100644
--- a/include/u.h
+++ b/include/u.h
@@ -92,6 +92,7 @@
 #	undef _NEEDUINT
 #	undef _NEEDULONG
 #elif defined(__OpenBSD__)
+#	include <sys/types.h>
 #	undef _NEEDUSHORT
 #	undef _NEEDUINT
 #	undef _NEEDULONG