add openbsd support

Author: niamtokik

src/pc_port_env.erl

@@ -303,7 +303,9 @@ default_env() ->
       lists:concat([" /LIBPATH:$ERL_EI_LIBDIR "] ++
                     [EiLib++".lib " || EiLib <- ErlInterfaceLibs])},
      {"win32", "DRV_CFLAGS", "/Zi /Wall $ERL_CFLAGS"},
-     {"win32", "DRV_LDFLAGS", "/DLL $ERL_LDFLAGS"}
+     {"win32", "DRV_LDFLAGS", "/DLL $ERL_LDFLAGS"},
+
+     {"openbsd", "CXX", "c++"}
     ].
 
 get_tool(Arch, Tool, Default) ->