Add Futhark IR module.

Not used for anything, but compiled as part of the Dex compiler.

Author: athas

dex.cabal

@@ -55,6 +55,7 @@ library
                      , Core
                      , Err
                      , Export
+                     , Futhark.IR
                      , Generalize
                      , Imp
                      , ImpToLLVM
@@ -111,6 +112,7 @@ library
                      , containers
                      , cryptonite
                      , exceptions
+                     , half
                      , hashable
                      , llvm-hs
                      , llvm-hs-pure