Add OpenBSD.

Index: runtime/druntime/src/rt/sections_ldc.d
--- runtime/druntime/src/rt/sections_ldc.d.orig
+++ runtime/druntime/src/rt/sections_ldc.d
@@ -30,6 +30,7 @@ else version (Darwin) {}
 else version (FreeBSD) {}
 else version (DragonFlyBSD) {}
 else version (NetBSD) {}
+else version (OpenBSD) {}
 else version (Windows) {}
 else version (LDC):
 
