[PATCH] Improve debugging output when there is a null function pointer in the IR dump.

[Richard Trieu]

> However, is this the best reporting we could give?  From what I can gather, null function means either an indirect call or the external function node in the callgraph.   Given the purpose of this pass, would simply skipping the null node entirely be clearer?  

I'm committed my patch.  I don't have any answers since I don't this part of LLVM.  Someone who regularly works with the optimizations would be able to answer which approach would be the most useful.

http://reviews.llvm.org/D4262