RFC: Simplify rules for ctz/clz patterns and RTL

[Jan Hubicka]

> 
> Is popcount really slow on PowerPC?  (Compared to clz?)  Ideally one 
> would choose between the two expansions based on RTL costs, but the only 
>  architectures it matters for are i386 and powerpc, and neither of them 
> define the cost of either clz or popcount.

Of course adding a popcount/clz cost into i386 cost tables is easy and
probably most correct thing to do :)

Honza
> 
> zw