${m} ARCH=${ARCH} >&!make_${m} を作成

~からマニュアルページ（tcshの場合）：

   > name
   >! name
   >& name
   >&! name
           The file name is used as standard output.  If the file does not
           exist then it is created; if the file exists, it is  truncated,
           its previous contents being lost.

           If  the shell variable noclobber is set, then the file must not
           exist or be a character  special  file  (e.g.,  a  terminal  or
           `/dev/null')  or an error results.  This helps prevent acciden‐
           tal destruction of files.  In this case the `!'  forms  can  be
           used to suppress this check.

           The  forms  involving  `&' route the diagnostic output into the
           specified file  as  well  as  the  standard  output.   name  is
           expanded in the same way as `<' input filenames are

だからリダイレクトされます標準出力そして標準エラー指定したファイルに移動してnoclobber確認を無視します。