[committed] prune out expected warning [PR104103]

[Martin Sebor]

The regression test gcc.dg/torture/pr57147-2.c triggers a valid
warning by passing a variable with zero size to a function that
expects an array of size 1.  The recent change to run the access
pass also earlier in the optimization pipeline has triggered
this warning.  In r12-6713 I have committed a change to prune
the warning out.

https://gcc.gnu.org/g:282110ae8b54250c8dcb73afc6f30761a41e38e6

I saw the test failure in my build before committing the original
change but then couldn't reproduce it so I chalked it up to cosmic
rays without deeper investigation.  My bad.

Martin