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This involved removing the old constant handling mechanism
which was fairly hard to use. Now being constant or not is
simply a property of a global variable instead of a separate
type.

We do this through a gnu as feature called subsections,
where you can put data/code into a numbered subsection
and those subsections will be joined together in descending
order by gas at compile time.

This was done as part of an honours thesis at UNSW, the paper describing the
work and results can be found at:

http://www.cse.unsw.edu.au/~pls/thesis/davidt-thesis.pdf

A Homepage for the backend can be found at:

http://hackage.haskell.org/trac/ghc/wiki/Commentary/Compiler/Backends/LLVM

Quick summary of performance is that for the 'nofib' benchmark suite, runtimes
are within 5% slower than the NCG and generally better than the C code
generator.  For some code though, such as the DPH projects benchmark, the LLVM
code generator outperforms the NCG and C code generator by about a 25%
reduction in run times.