[PATCH] Fix PR17687 sincos -> cexp canonicalization (2nd try)

[Paolo Bonzini]

> even a pass doing proper
> gimplification on a folded tree will hit the ICE as we have in build2
> 
>   if (code == MODIFY_EXPR && cfun && cfun->gimplified)
>     {
>       /* We should be talking GIMPLE_MODIFY_STMT by now.  */
>       gcc_unreachable ();
>     }
> 
> which is IMHO broken.  This is more for verify_stmts.

Agreed; or for tsi_link_{before,after}.

Paolo