[4.4 PATCH] Fix ipa-cp ICE (PR tree-optimization/42890)

[Jan Hubicka]

> Hi!
> 
> This ICEs because tree_function_versioning calls delete_unreachable_blocks
> which removes some unreachable calls, but nothing removes corresponding cg
> edges, so ipa-cp looks at type of freed SSA names.
> Seems the trunk has for this a new function which handles updating of the
> callgraph, on the 4.4 branch as delete_unreachable_blocks is only called
> when !update_clones we can leave out big part of that function though.
> 
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for the 4.4 branch?
Yep, that works for me too (as well as the variant of rebuilding edges I
suggsted elsewhere).

Honza