[PING][PATCH] adjust "partly out of bounds" warning (PR 98503)

[Martin Sebor]

Ping:
https://gcc.gnu.org/pipermail/gcc-patches/2021-January/564483.html

The review of this patch digressed into a design discussion of a new,
more capable implementation of -Wstrict-aliasing, but the proposed
patch turning just this one instance of -Warray-bounds into
-Wstrict-aliasing and making it subject to -fstrict-aliasing wasn't
decided.  PR 98503 was raised by someone working with the kernel
which uses -fno-strict-aliasing, and so to them the warning isn't
useful.  But since the warning does find potential bugs when strict
aliasing is in effect, I'd still like to consider this patch for
GCC 11 so that the kernel (and other such projects) doesn't have
to deal with the false positives.

If/when we add a new, dedicated solution for -Wstrict-aliasing I'll
move this instance from gimple-array-bounds.cc there.

Martin