Add support for detecting the primordial thread

Index: src/hotspot/share/runtime/os.hpp
--- src/hotspot/share/runtime/os.hpp.orig
+++ src/hotspot/share/runtime/os.hpp
@@ -508,7 +508,7 @@ class os: AllStatic {
   // need special-case handling of the primordial thread if it attaches
   // to the VM.
   static bool is_primordial_thread(void)
-#if defined(_WINDOWS) || defined(BSD)
+#if defined(_WINDOWS) || (defined(BSD) && !defined(__OpenBSD__))
     // No way to identify the primordial thread.
     { return false; }
 #else
