threads: test for sys/param.h and include it for sysctl on OpenBSD

configure

@@ -1140,6 +1140,7 @@ HAVE_LIST="
     symver_gnu_asm
     sysctl
     sys_mman_h
+    sys_param_h
     sys_resource_h
     sys_select_h
     sys_soundcard_h
@@ -2871,6 +2872,7 @@ check_header dxva2api.h
 check_header malloc.h
 check_header poll.h
 check_header sys/mman.h
+check_header sys/param.h
 check_header sys/resource.h
 check_header sys/select.h
 check_header vdpau/vdpau.h

libavcodec/pthread.c

@@ -37,6 +37,9 @@
 #elif HAVE_GETSYSTEMINFO
 #include <windows.h>
 #elif HAVE_SYSCTL
+#if HAVE_SYS_PARAM_H
+#include <sys/param.h>
+#endif
 #include <sys/types.h>
 #include <sys/sysctl.h>
 #endif