Defining Multiple targets in a make file

If I wanted to define different targets in a make file were the source code would look like shown below:

#if    defined(_485_HEAD_)

#include "system.h"
#include "string.h"
#include "mem_mgr.h"

typedef long              s32;
typedef unsigned long     u32;
typedef int               s16;
typedef unsigned int      u16;
typedef char              s8;
typedef unsigned char     u8;
typedef unsigned char        boolean;



#elif defined(_485_RELAY_)

etc......
#endif

How would I tell the make file to use directive "485_RELAY" or "485_HEAD"?