[haskell-llvm] string creation

[Henning Thielemann]

I had experimentally added (Nat n) to some array functions. That spotted a 
problem in LLVM.Core.CodeGen.string. The 'string' function creates an 
array constant for a string and returns an Array type of undetermined 
size. There is no check, that the array type has the correct size. How 
about using type-level's reifyIntegral and continuation passing style in 
order to provide an Array type with the correct size?