bug#10164: 24.0.91; Instant crash enabling linum-mode

[Eli Zaretskii]

> Date: Tue, 29 Nov 2011 19:05:20 -0700
> From: Tim Crews <tim.crews@code-affinity.com>
> 
>     Start Emacs with runemacs -Q --no-init-file
>     C-x C-f foo.txt
>     M-x linum-mode
>     (Emacs doesn't crash yet)
>     Type anything.  Emacs instantly crashes.

Arrgh!  This is GCC 4.6.x "as-is" code reordering in action.  Emacs
crashes here:

              xassert (!row->enabled_p
                       || row->mode_line_p
                       || verify_row_hash (row));

Evidently, it calls verify_row_hash before it tests row->mode_line_p.