Generate a c-shared library for the standard C LLVM API

[mewmew]

This idea was originally presented by @quarnster in https://github.com/llir/llvm/issues/3#issuecomment-122688309. Creating a dedicated issue to track any discussions on the LLVM-dev mailing list, and implementation discussions. Please post updates in this issue if you read about the direction in which the definition of a stable C LLVM API is heading (this is still an active topic of discussion).

With go 1.5's support for creating c-shared libraries, I really like the idea of having a go generate tool which generates the standard C LLVM api (or the implemented subset anyways). That way this code could be used as a drop in replacement for anything that currently uses the LLVM C api, presuming all the functions used are implemented.

Just figured I'd mention this as it's been on my mind due to the discussion on the llvm-dev list about potentially splitting the LLVM C api into a separate project.