Fix benchmarks

[yebai]

Fixed some minor issues in benchmarks. It now runs but produces the error below

julia> benchmark_driver!(rosenbrock, x)

       ####################################################################
benchmarking rosenbrock...
ERROR: Unhandled stmt $(Expr(:loopinfo, Symbol("julia.simdloop"), nothing)) of type Expr
Stacktrace:
  [1] error(s::String)
    @ Base ./error.jl:35
  [2] (::Libtask.var"#14#26"{…})(::Tuple{…})
    @ Libtask ~/.julia/packages/Libtask/Aw9k4/src/copyable_task.jl:708
  [3] iterate
    @ ./generator.jl:48 [inlined]
  [4] collect(itr::Base.Generator{Base.Iterators.Enumerate{…}, Libtask.var"#14#26"{…}})
    @ Base ./array.jl:791
  [5] map
    @ ./abstractarray.jl:3399 [inlined]
  [6] (::Libtask.var"#13#25"{…})(::Tuple{…})
    @ Libtask ~/.julia/packages/Libtask/Aw9k4/src/copyable_task.jl:552
  [7] iterate
    @ ./generator.jl:48 [inlined]
  [8] collect_to!(dest::Vector{…}, itr::Base.Generator{…}, offs::Int64, st::Tuple{…})
    @ Base ./array.jl:849
  [9] collect_to_with_first!(dest::Vector{…}, v1::Vector{…}, itr::Base.Generator{…}, st::Tuple{…})
    @ Base ./array.jl:827
 [10] collect(itr::Base.Generator{Base.Iterators.Zip{…}, Libtask.var"#13#25"{…}})
    @ Base ./array.jl:801
 [11] map(f::Function, A::Base.Iterators.Zip{Tuple{Vector{Libtask.BasicBlockCode.BBlock}, Vector{Vector{…}}, Vector{Vector{…}}}})
    @ Base ./abstractarray.jl:3399
 [12] derive_copyable_task_ir(ir::Libtask.BasicBlockCode.BBCode)
    @ Libtask ~/.julia/packages/Libtask/Aw9k4/src/copyable_task.jl:551
 [13] build_callable(sig::Type{Tuple{typeof(rosenbrock), Vector{Float64}, Nothing}})
    @ Libtask ~/.julia/packages/Libtask/Aw9k4/src/copyable_task.jl:59
 [14] TapedTask(::Nothing, ::Function, ::Vararg{Any}; kwargs::@Kwargs{})
    @ Libtask ~/.julia/packages/Libtask/Aw9k4/src/copyable_task.jl:202
 [15] TapedTask(::Nothing, ::Function, ::Vararg{Any})
    @ Libtask ~/.julia/packages/Libtask/Aw9k4/src/copyable_task.jl:199
 [16] benchmark_driver!(f::Function, x::Vector{Float64}; f_displayname::String)
    @ Main ./REPL[4]:5
 [17] benchmark_driver!(f::Function, x::Vector{Float64})
    @ Main ./REPL[4]:1
 [18] top-level scope
    @ REPL[7]:1
Some type information was truncated. Use `show(err)` to see complete types.

[willtebbutt]

Thanks for this -- the error is something that needs fixing in the main PR (it's just an IR instruction that we haven't explicitely written out support for yet).

I'll merge this into my PR.