stub thread affinity stuff

Index: rts/System/Platform/ThreadAffinityGuard.h
--- rts/System/Platform/ThreadAffinityGuard.h.orig
+++ rts/System/Platform/ThreadAffinityGuard.h
@@ -13,7 +13,9 @@ class ThreadAffinityGuard { (private)
 	DWORD_PTR savedAffinity;
 	HANDLE threadHandle;
 #else
+#ifndef __OpenBSD__
 	cpu_set_t savedAffinity;
+#endif
 	pid_t tid;
 #endif
 	bool affinitySaved;
