improve portability of Makefile
improve portability of Makefile

Ignore-this: a73a9ea992d817a084a75b6e47d516ae

darcs-hash:20100711054513-1a7c6-5769f99a5426af6163fae016487ae0fefe79de96

kirbyfan64/jhc,kirbyfan64/jhc,kirbyfan64/jhc,kirbyfan64/jhc