Fix Makefile for OSX

Bump base SDK from 10.5 -> 10.7
Just use the builtin __APPLE__

code/qcommon/qcommon.h

@@ -1108,7 +1108,7 @@ void	Sys_SetDefaultInstallPath(const char *path);
 char	*Sys_DefaultInstallPath(void);
 char	*Sys_SteamPath(void);
 
-#ifdef MACOS_X
+#ifdef __APPLE__
 char    *Sys_DefaultAppPath(void);
 #endif