move tags into globally accesible table, so we don't have to overload the getSystemTags method all over the place.

src/base/os.lua

@@ -720,8 +720,7 @@
 -- Get a set of tags for different 'platforms'
 --
 
-	function os.getSystemTags(name)
-		local tags =
+	os.systemTags =
 	{
 		["aix"]      = { "aix",     "posix" },
 		["bsd"]      = { "bsd",     "posix" },
@@ -731,5 +730,7 @@
 		["solaris"]  = { "solaris", "posix" },
 		["windows"]  = { "windows", "win32" },
 	}
-		return tags[name] or name
+
+	function os.getSystemTags(name)
+		return os.systemTags[name] or name
 	end