[committed 2.35] fortify: Ensure that __glibc_fortify condition is a constant [BZ #29141]

[Siddhesh Poyarekar]

On 16/05/2022 21:40, Siddhesh Poyarekar via Libc-stable wrote:
> The fix c8ee1c85 introduced a -1 check for object size without also
> checking that object size is a constant.  Because of this, the tree
> optimizer passes in gcc fail to fold away one of the branches in
> __glibc_fortify and trips on a spurious Wstringop-overflow.  The warning
> itself is incorrect and the branch does go away eventually in DCE in the
> rtl passes in gcc, but the constant check is a helpful hint to simplify
> code early, so add it in.
> 
> Resolves: BZ #29141
> Signed-off-by: Siddhesh Poyarekar <siddhesh@sourceware.org>

Ugh, I'm so sorry, I forgot to use -x :(

We should have a commit hook that rejects patches on release branches 
without the "cherry picked from".

Siddhesh