[yara] build fixes, and use FOR_BB_INSNS where possible

[Vladimir N. Makarov]

Steven Bosscher wrote:

>Hi Vlad, all,
>
>With this patch, I can bootstrap the compilers for c,c++,fortran on x86_64,
>though I still can't do a full bootstrap because of an ICE in lower-subreg.
>But it's progress compared to earlier today, when I had lots of warnings
>and even a normal build wouldn't work.
>
>This also cleans up a few places to use FOR_BB_INSNS instead of a special
>loop.
>
>Vlad, can you put this  on the yara-branch if it looks good to you?
>
>  
>
Steven, thanks for the patch.  I've put it on the branch.