improve the autoconf warning for broken readdir

configure.in

@@ -75,7 +75,7 @@ AC_TRY_RUN([#include <sys/types.h>
 main() { struct dirent *di; DIR *d = opendir("."); di = readdir(d);
 if (di && di->d_name[-2] == '.' && di->d_name[-1] == 0 &&
 di->d_name[0] == 0) return 0; return 1;} ],
-echo yes;AC_DEFINE(HAVE_BROKEN_READDIR), 
+echo yes - you are using the broken /usr/ucb/cc;AC_DEFINE(HAVE_BROKEN_READDIR), 
 echo no)
 
 echo $ac_n "checking for utimbuf ... $ac_c"