Generate debug info for generics

[jdm]

The debug info generator is almost certain to fall over if it comes across generic functions or types. This should be rectified (presumably using the metadata facilities for dealing with C++ templates).

[marijnh]

I'm currently working on #1736 -- if that works out, along with cross-crate inlining/monomorphizing, this issue will be much easier to tackle. So unless this is really getting in someone's way, I would recommend you don't work on it on the short term.

[msullivan]

Now that we monomorphize, what is the status of this?

[jdm]

We probably want to generate metadata that includes template information now. Clang's probably the best reference for this, since http://llvm.org/docs/SourceLevelDebugging.html#format_subprograms doesn't give any example of what's expected.

[emberian]

/cc @michaelwoerister