syscall: regenerate z-files for openbsd

This CL restores dropped constants not supported in OpenBSD 5.5
and tris to keep the promise of API compatibility.

Update #7049

LGTM=jsing, bradfitz, rsc
R=rsc, jsing, robert.hencke, minux.ma, bradfitz, iant
CC=golang-codereviews
https://golang.org/cl/96970043
3 files changed