`nested task error: unsupported or misplaced expression aliasscope` when using `julia --compile=min`

I recently tried using the `julia --compile=min` flag to spend less time compiling (and more time debugging) but KernelAbstractions.jl started erroring.

Turns out I can reproduce the same error by running the simple `memcopy.jl` example: https://github.com/JuliaGPU/KernelAbstractions.jl/blob/8c9d7b48fb3b9dbecc5aae7e30e2758f2f71b6d5/examples/memcopy.jl

Couldn't find the `--compile` flag mentioned in `julia --help` so maybe it's an internal flag I shouldn't be using.

```
$ julia --project --compile=min ─╯
_
_ _ _(_)_ | Documentation: https://docs.julialang.org
(_) | (_) (_) |
_ _ _| |_ __ _ | Type "?" for help, "]?" for Pkg help.
| | | | | | |/ _` | |
| | |_| | | | (_| | | Version 1.6.0 (2021-03-24)
_/ |\__'_|_|_|\__'_| | Official https://julialang.org/ release
|__/ |

julia> include("examples/memcopy.jl")
ERROR: LoadError: TaskFailedException
Stacktrace:
[1] wait(t::Task)
@ Base task.jl:317
[2] wait(::CPU, ev::KernelAbstractions.CPUEvent, progress::Nothing)
@ KernelAbstractions ~/KernelAbstractions.jl/src/cpu.jl:65
[3] wait(ev::KernelAbstractions.CPUEvent, progress::Nothing) (repeats 2 times)
@ KernelAbstractions ~/KernelAbstractions.jl/src/cpu.jl:29
[4] top-level scope
@ ~/KernelAbstractions.jl/examples/memcopy.jl:20
[5] include(fname::String)
@ Base.MainInclude client.jl:444
[6] top-level scope
@ REPL[1]:1

nested task error: unsupported or misplaced expression aliasscope
Stacktrace:
[1] cpu_copy_kernel!(::Matrix{Float64}, ::Matrix{Float64})
@ none:0 [inlined]
[2] overdub(::Cassette.Context{nametype(CPUCtx), KernelAbstractions.CompilerMetadata{KernelAbstractions.NDIteration.DynamicSize, KernelAbstractions.NDIteration.NoDynamicCheck, CartesianIndex{1}, CartesianIndices{1, Tuple{Base.OneTo{Int64}}}, KernelAbstractions.NDIteration.NDRange{1, KernelAbstractions.NDIteration.DynamicSize, KernelAbstractions.NDIteration.StaticSize{(8,)}, CartesianIndices{1, Tuple{Base.OneTo{Int64}}}, Nothing}}, Nothing, KernelAbstractions.var"##PassType#257", Nothing, Cassette.DisableHooks}, ::typeof(cpu_copy_kernel!), ::Matrix{Float64}, ::Matrix{Float64})
@ Cassette none:0
[3] __thread_run(tid::Int64, len::Int64, rem::Int64, obj::KernelAbstractions.Kernel{CPU, KernelAbstractions.NDIteration.StaticSize{(8,)}, KernelAbstractions.NDIteration.DynamicSize, typeof(cpu_copy_kernel!)}, ndrange::Tuple{Int64}, iterspace::KernelAbstractions.NDIteration.NDRange{1, KernelAbstractions.NDIteration.DynamicSize, KernelAbstractions.NDIteration.StaticSize{(8,)}, CartesianIndices{1, Tuple{Base.OneTo{Int64}}}, Nothing}, args::Tuple{Matrix{Float64}, Matrix{Float64}}, dynamic::KernelAbstractions.NDIteration.NoDynamicCheck)
@ KernelAbstractions ~/KernelAbstractions.jl/src/cpu.jl:157
[4] __run(obj::KernelAbstractions.Kernel{CPU, KernelAbstractions.NDIteration.StaticSize{(8,)}, KernelAbstractions.NDIteration.DynamicSize, typeof(cpu_copy_kernel!)}, ndrange::Tuple{Int64}, iterspace::KernelAbstractions.NDIteration.NDRange{1, KernelAbstractions.NDIteration.DynamicSize, KernelAbstractions.NDIteration.StaticSize{(8,)}, CartesianIndices{1, Tuple{Base.OneTo{Int64}}}, Nothing}, args::Tuple{Matrix{Float64}, Matrix{Float64}}, dynamic::KernelAbstractions.NDIteration.NoDynamicCheck)
@ KernelAbstractions ~/KernelAbstractions.jl/src/cpu.jl:130
[5] (::KernelAbstractions.var"#33#34"{Nothing, Nothing, typeof(KernelAbstractions.__run), Tuple{KernelAbstractions.Kernel{CPU, KernelAbstractions.NDIteration.StaticSize{(8,)}, KernelAbstractions.NDIteration.DynamicSize, typeof(cpu_copy_kernel!)}, Tuple{Int64}, KernelAbstractions.NDIteration.NDRange{1, KernelAbstractions.NDIteration.DynamicSize, KernelAbstractions.NDIteration.StaticSize{(8,)}, CartesianIndices{1, Tuple{Base.OneTo{Int64}}}, Nothing}, Tuple{Matrix{Float64}, Matrix{Float64}}, KernelAbstractions.NDIteration.NoDynamicCheck}})()
@ KernelAbstractions ~/KernelAbstractions.jl/src/cpu.jl:22
in expression starting at /home/alir/KernelAbstractions.jl/examples/memcopy.jl:20
```

Environment:

```
julia> versioninfo()
Julia Version 1.6.0
Commit f9720dc2eb (2021-03-24 12:55 UTC)
Platform Info:
OS: Linux (x86_64-pc-linux-gnu)
CPU: Intel(R) Core(TM) i7-7700HQ CPU @ 2.80GHz
WORD_SIZE: 64
LIBM: libopenlibm
LLVM: libLLVM-11.0.1 (ORCJIT, skylake)
```

```
(KernelAbstractions) pkg> st
Project KernelAbstractions v0.6.0
Status `~/KernelAbstractions.jl/Project.toml`
[79e6a3ab] Adapt v3.2.0
[72cfdca4] CUDAKernels v0.1.0 `lib/CUDAKernels`
[7057c7e9] Cassette v0.3.5
[1914dd2f] MacroTools v0.5.6
[276daf66] SpecialFunctions v1.3.0
[90137ffa] StaticArrays v1.1.0
[b77e0a4c] InteractiveUtils
[cf7118a7] UUIDs
```

Reproduce with Julia 1.6.0 using --project --compile=min and examples/memcopy.jl. Trace the failure through src/cpu.jl, including wait and __thread_run, and the Cassette overdub shown in the stack trace; done means the example runs without the aliasscope TaskFailedException under this flag.

Written by the indexing model from the issue text.