gcc/Makefile.in targets 'compare' and 'gnucompare' behave differently

[DJ Delorie]

>   for file in *.o; do \
>     test -f stage$stage/$file && (cmp --ignor...bad_compare) || true; \
>   done

That adds back in some of the overhead, unless we assume that the
shell is running the test command internally.  Otherwise, I can't
think of a better way, unless we can check for cmp's exit code being
exactly 1 (it returns 2 if one of the files is missing).