Simple hello world example fails with JuliaC using --experimental --trim

I've been playing around with [JuliaC](https://github.com/JuliaLang/JuliaC.jl) and thought I would give a simple ```MPI.jl``` example a go. This is a simple adaptation of [this Hello, World! example](https://juliaparallel.org/MPI.jl/stable/examples/01-hello/)

```julia
using MPI

function @main(ARGS)
MPI.Init()
comm = MPI.COMM_WORLD
print(Core.stdout, "Hello world, I am rank $(MPI.Comm_rank(comm)) of $(MPI.Comm_size(comm))\n")
return 0
end
```

Without ```--experimental --trim=safe``` everything works as expected with a binary size of around 300MB.

However, with ```--experimental --trim=safe``` we get the following errors

```
Compiling...Verifier error #1: unresolved call from statement (Base.memoryrefget(Base.memoryrefnew(Base.getfield(MPI.mpi_init_hooks, :ref)::MemoryRef{Any}, 1, false::Bool)::MemoryRef{Any}, :not_atomic, false::Bool)::Any)()::Any
Stacktrace:
[1] run_init_hooks()
@ MPI ~/.julia/packages/MPI/hNJm0/src/environment.jl:66
[2] Init(; threadlevel::Symbol, finalize_atexit::Bool, errors_return::Bool)
@ MPI ~/.julia/packages/MPI/hNJm0/src/environment.jl:155
[3] Init()
@ MPI ~/.julia/packages/MPI/hNJm0/src/environment.jl:114 [inlined]
[4] main(ARGS::Vector{String})
@ Main ~/Cthonios/ParaTaxi/examples/src/HelloWorld.jl:4
[5] _main(argc::Int32, argv::Ptr{Ptr{Int8}})
@ Main ~/.julia/packages/JuliaC/EFQEY/src/scripts/juliac-buildscript.jl:77

Verifier error #2: unresolved call from statement (f::typeof(MPI.call))(φ ()::Any)::Any
Stacktrace:
[1] foreach(f::typeof(MPI.call), itr::Vector{Any})
@ Base abstractarray.jl:3188
[2] run_load_time_hooks()
@ MPI ~/.julia/packages/MPI/hNJm0/src/MPI.jl:74
[3] __init__()
@ MPI ~/.julia/packages/MPI/hNJm0/src/MPI.jl:174

Verifier error #3: unresolved call from statement (%new()::MPI.var"#copy#copy##0"{MPI.OpWrapper{typeof(xor), Any}, Ptr{Nothing}, Ptr{Nothing}, Int32})(MPI.to_type(%new()::MPI.Datatype)::Any)::Any
Stacktrace:
[1] (::MPI.OpWrapper{typeof(xor), Any})(_a::Ptr{Nothing}, _b::Ptr{Nothing}, _len::Ptr{Int32}, t::Ptr{Int32})
@ MPI ~/.julia/packages/MPI/hNJm0/src/operators.jl:98

Verifier error #4: unresolved call from statement (%new()::MPI.var"#copy#copy##0"{MPI.OpWrapper{typeof(|), Any}, Ptr{Nothing}, Ptr{Nothing}, Int32})(MPI.to_type(%new()::MPI.Datatype)::Any)::Any
Stacktrace:
[1] (::MPI.OpWrapper{typeof(|), Any})(_a::Ptr{Nothing}, _b::Ptr{Nothing}, _len::Ptr{Int32}, t::Ptr{Int32})
@ MPI ~/.julia/packages/MPI/hNJm0/src/operators.jl:98

Verifier error #5: unresolved call from statement (%new()::MPI.var"#copy#copy##0"{MPI.OpWrapper{typeof(&), Any}, Ptr{Nothing}, Ptr{Nothing}, Int32})(MPI.to_type(%new()::MPI.Datatype)::Any)::Any
Stacktrace:
[1] (::MPI.OpWrapper{typeof(&), Any})(_a::Ptr{Nothing}, _b::Ptr{Nothing}, _len::Ptr{Int32}, t::Ptr{Int32})
@ MPI ~/.julia/packages/MPI/hNJm0/src/operators.jl:98

Verifier error #6: unresolved call from statement (%new()::MPI.var"#copy#copy##0"{MPI.OpWrapper{typeof(*), Any}, Ptr{Nothing}, Ptr{Nothing}, Int32})(MPI.to_type(%new()::MPI.Datatype)::Any)::Any
Stacktrace:
[1] (::MPI.OpWrapper{typeof(*), Any})(_a::Ptr{Nothing}, _b::Ptr{Nothing}, _len::Ptr{Int32}, t::Ptr{Int32})
@ MPI ~/.julia/packages/MPI/hNJm0/src/operators.jl:98

Verifier error #7: unresolved call from statement (%new()::MPI.var"#copy#copy##0"{MPI.OpWrapper{typeof(+), Any}, Ptr{Nothing}, Ptr{Nothing}, Int32})(MPI.to_type(%new()::MPI.Datatype)::Any)::Any
Stacktrace:
[1] (::MPI.OpWrapper{typeof(+), Any})(_a::Ptr{Nothing}, _b::Ptr{Nothing}, _len::Ptr{Int32}, t::Ptr{Int32})
@ MPI ~/.julia/packages/MPI/hNJm0/src/operators.jl:98

Verifier error #8: unresolved call from statement (%new()::MPI.var"#copy#copy##0"{MPI.OpWrapper{typeof(max), Any}, Ptr{Nothing}, Ptr{Nothing}, Int32})(MPI.to_type(%new()::MPI.Datatype)::Any)::Any
Stacktrace:
[1] (::MPI.OpWrapper{typeof(max), Any})(_a::Ptr{Nothing}, _b::Ptr{Nothing}, _len::Ptr{Int32}, t::Ptr{Int32})
@ MPI ~/.julia/packages/MPI/hNJm0/src/operators.jl:98

Verifier error #9: unresolved call from statement (%new()::MPI.var"#copy#copy##0"{MPI.OpWrapper{typeof(min), Any}, Ptr{Nothing}, Ptr{Nothing}, Int32})(MPI.to_type(%new()::MPI.Datatype)::Any)::Any
Stacktrace:
[1] (::MPI.OpWrapper{typeof(min), Any})(_a::Ptr{Nothing}, _b::Ptr{Nothing}, _len::Ptr{Int32}, t::Ptr{Int32})
@ MPI ~/.julia/packages/MPI/hNJm0/src/operators.jl:98

Verifier error #10: unresolved call from statement (Base.memoryrefget(Base.memoryrefnew(Base.getfield(MPI.mpi_init_hooks, :ref)::MemoryRef{Any}, 1, false::Bool)::MemoryRef{Any}, :not_atomic, false::Bool)::Any)()::Any
Stacktrace:
[1] run_init_hooks()
@ MPI ~/.julia/packages/MPI/hNJm0/src/environment.jl:66
[2] Init(; threadlevel::Symbol, finalize_atexit::Bool, errors_return::Bool)
@ MPI ~/.julia/packages/MPI/hNJm0/src/environment.jl:155
[3] Init()
@ MPI ~/.julia/packages/MPI/hNJm0/src/environment.jl:114 [inlined]
[4] main(ARGS::Vector{String})
@ Main ~/Cthonios/ParaTaxi/examples/src/HelloWorld.jl:4
◐ Compiling..._main(argc::Int32, argv::Ptr{Ptr{Int8}})
@ Main ~/.julia/packages/JuliaC/EFQEY/src/scripts/juliac-buildscript.jl:77

Trim verify finished with 10 errors, 0 warnings.
✓ Compiling...
ERROR: LoadError: Failed to compile src/HelloWorld.jl
Stacktrace:
[1] error(s::String)
@ Base ./error.jl:44
[2] compile_products(recipe::ImageRecipe)
@ JuliaC ~/.julia/packages/JuliaC/EFQEY/src/compiling.jl:142
[3] top-level scope
@ ~/Cthonios/ParaTaxi/examples/build.jl:24
[4] include(mod::Module, _path::String)
@ Base ./Base.jl:306
[5] exec_options(opts::Base.JLOptions)
@ Base ./client.jl:317
[6] _start()
@ Base ./client.jl:550
```

From what I can gather through looking through the ```src``` code, it looks like there's an array of functions at the module level that are run during ```MPI.Init()``` that leads to these unresolved calls.

I'm happy to help put effort into fixing this currently *niche* use case, but thought I would open an issue first to see if the maintainers have any qualms before putting effort in.

It would be great to bring small binaries with MPI to the community!