[PATCH] ELF: Add a standard method for unknown relocation errors

[Will Newton]

>>! In D6523#6, @atanasyan wrote:
> Good idea. Did you consider to factor out the `unhandledReferenceType` method into the separate class? Some sort of `Diagnostic`. The `LinkingContext` might have a reference to this class. That allow us to keep all diagnostics stuff together and simplify implementation of  feature-rich diagnostics engine in the future.

I noticed that there is the issue of diagnostics to be resolved on the projects list. It is something that should be done I think but at the moment I am not sure I know what it would look like an dhopefully this change can be an incremental step that work easier in future.

I found a couple of bugs in cc-mode that were causing the indentation to be wrong. Hopefully these are all now fixed.

http://reviews.llvm.org/D6523