the last parameter of XChangeProperty is the number of elements.. and when the element format is 32.. the element is "long" so we have 5 long elements here.

Yes this seems confusing as on mac+linux Long is either 32 or 64bits depending on the architecture, but this is how the X11 protocol is defined. Thus 5 is the correct value for the nelts here.  Not 5 or 10 depending on the architecture.

More info on the confusion https://bugs.freedesktop.org/show_bug.cgi?id=16802

premake/projects/SDL2main.lua

@@ -0,0 +1,31 @@
+-- Copyright (C) 1997-2014 Sam Lantinga <slouken@libsdl.org>
+--
+-- This software is provided 'as-is', without any express or implied
+-- warranty.  In no event will the authors be held liable for any damages
+-- arising from the use of this software.
+--
+-- Permission is granted to anyone to use this software for any purpose,
+-- including commercial applications, and to alter it and redistribute it
+-- freely.
+--
+-- Meta-build system using premake created and maintained by
+-- Benjamin Henning <b.henning@digipen.edu>
+
+--[[
+SDL2main.lua
+
+	This file defines the SDL2main project which builds the SDL2main static
+	library for Windows and Mac. This project is primarily for everything but
+	Linux.
+]]
+
+SDL_project "SDL2main"
+	SDL_kind "StaticLib"
+	SDL_language "C"
+	SDL_sourcedir "../src"
+	SDL_dependency "windows"
+		SDL_os "windows|mingw"
+		SDL_paths { "/main/windows/" }
+	SDL_dependency "macosx or ios"
+		SDL_os "macosx|ios|cygwin"
+		SDL_paths { "/main/dummy/" }