Fix PR34916, 35519 Combine (Dataflow merge regression.)

[Paolo Bonzini]

> The log_links list  being walked is very short - only one element per 
> immediately linked instruction. So typical length is perhaps 2 (without 
> duplicates). The largest would be for an instruction which has many 
> input operands where each is the output of an instructions in same 
> block, with no intervening usage.   Maybe a libcall call of some type.  
> But still short list!

I agree, create_log_links doesn't even add LOG_LINKS to asms, which 
potentially have a lot of uses.  I think this is entirely comparable to 
using insertion sort because you know the size of the array is small.

I cannot approve this though (and would not like to override Richi anyway).

Paolo