BUILD: makefile: Update feature flags for OpenBSD

Update the OpenBSD target features being enabled.

I updated the list of features after noticing
"BUILD: makefile: disable threads by default on OpenBSD".

The Makefile utilizing gcc(1) by default resulted in utilizing
our legacy and obsolete compiler (GCC 4.2.1) instead of the
proper system compiler (Clang), which does support TLS. With
"BUILD: makefile: change default value of CC from gcc to cc"
that is resolved.
diff --git a/Makefile b/Makefile
index 934ca16..197126d 100644
--- a/Makefile
+++ b/Makefile
@@ -377,10 +377,11 @@
   EXPORT_SYMBOL  = -export_dynamic
 endif
 
-# OpenBSD 5.7 and above
+# OpenBSD 6.3 and above
 ifeq ($(TARGET),openbsd)
   set_target_defaults = $(call default_opts, \
-    USE_POLL USE_TPROXY USE_KQUEUE USE_ACCEPT4)
+    USE_POLL USE_TPROXY USE_THREAD USE_KQUEUE USE_ACCEPT4 USE_CLOSEFROM   \
+    USE_GETADDRINFO)
 endif
 
 # NetBSD