Attempted to add LLVM 3.4 compatibility.

This is my admittedly probably awful attempt at adding compatibility to
Idris for LLVM v3.4.*.

There is a change to the cabal file to cater for either 3.3.8.* or
3.4.*.

There is also a change to the output function for writing the LLVM code
that needed a LLVM.General.Module.File type and not FilePath or String.

Not expecting this to be accepted but it might give someone who knows
what they are doing an idea...