bug#22074: unixware 7.1.4 rm command

[Karl Berry]

Hi Jarkko - back in 2015
(https://debbugs.gnu.org/cgi/bugreport.cgi?bug=22074, sorry for the
delayed reply) you reported that your system failed the rm -f test. 

For the next automake release, we've removed this test and tried to
accept any rm. (More info: https://bugs.gnu.org/10828.)

If you have a chance to try an automake pretest to confirm this
(downloadable from https://alpha.gnu.org/gnu/automake-1.16j.tar.gz),
that would be great. --thanks, karl.