let... in struct is not translated right

[tcr]

There are only a few instances of these in the codebase (see C.lhs) but it should be parsed properly at least.

    CIntConst (CInteger v repr flags) _ ->
        let allow_signed = not (testFlag FlagUnsigned flags)
            allow_unsigned = not allow_signed || repr /= DecRepr
            widths =
                [ (32 :: Int,
                    if any (`testFlag` flags) [FlagLongLong, FlagLong]
                    then WordWidth else BitWidth 32)
                , (64, BitWidth 64)
                ]
            allowed_types =
                [ IsInt s w
                | (bits, w) <- widths
                , (True, s) <- [(allow_signed, Signed), (allow_unsigned, Unsigned)]
                , v < 2 ^ (bits - if s == Signed then 1 else 0)
                ]
            repr' = case repr of
                DecRepr -> Rust.DecRepr
                OctalRepr -> Rust.OctalRepr
                HexRepr -> Rust.HexRepr
        in case allowed_types of
        [] -> badSource expr "integer (too big)"
        ty : _ -> return (literalNumber ty (Rust.LitInt v repr'))