bug#10828: [RFC] POSIX will say running "rm -f" with no argument is OK

[Karl Berry]

Hi Mike,

    the issue isn't `rm -f` exactly, it's `rm -f` with a variable that
    could be empty.

Sure.

    i'm not sure we need to fully audit the tree 

Seems desirable to make a best effort to look at every viable case.

At any rate, it should be reproducible on OpenSolaris etc., as reported
by Bob F earlier in this report. So I hope Bob could try any proposed
patches and check for missing cases.

    we could add a helper var to further collapse the boiler plate.
            am__rm_f = rm -f $(am__rm_f_notfound)
    then the rule is a bit more palatable:
            $(am__rm_f) ...

Personally I find making "rm -f" into a variable less readable
than the original suggestion of:
        rm -f ... $(am__rm_f_notfound)

The minor tweak that comes to my mind is that maybe the variable name
would be better as $(am__rm_f_notfound_file):
        rm -f ... $(am__rm_f_notfound_file)

    or if we want to claim namespace and make it something we want to export
    for users of automake akin to AC_PROG_LN_S, we could use RM_F.

Our hope/belief is that the proposed change would silently fix the
problem.  In which case I don't see a win to doing something in user
namespace, having to document it, etc.

(Incidentally, I'd never want to define a variable as simple as "RM_F"
at this late date. Too much chance of collision ... AM_RM_F would be ok
if we wanted to go this route, but, as I say, I don't see a reason at
the moment.) --thanks, karl.