Fix llvmcall overdubbing

[vchuravy]

First attempt at fixing #138

This is still not quite sufficient and the tests fail with:

  Got exception outside of a @test
  LoadError: error compiling recurse: error statically evaluating llvm IR argument: access to invalid slot number
  Stacktrace:
   [1] overdub(::Cassette.Context{nametype(LLVMCallCtx),Nothing,Nothing,getfield(Cassette, Symbol("##PassType#365")),Nothing,Nothing}, ::Function, ::Float64) at /home/vchuravy/src/Cassette/test/misctests.jl:683
   [2] recurse(::Cassette.Context{nametype(LLVMCallCtx),Nothing,Nothing,getfield(Cassette, Symbol("##PassType#365")),Nothing,Nothing}, ::getfield(Main, Symbol("##111#112"))) at /home/vchuravy/src/Cassette/src/overdub.jl:695
   [3] top-level scope at none:0

Inspired by https://github.com/vchuravy/GPUifyLoops.jl/blob/760700e12f88c4bebb072d5f0453bed1d24692a3/src/context.jl#L59-L87

I also tried to solve this by using various function overloads, but no joy.

[vchuravy]

cc: @oxinabox @NHDaly

[oxinabox]

this is super cute

[NHDaly]

I think this makes sense. We talked about this in person, but just recording here that this of course means that llvmcalls won't get overdubbed, so users who do want to make modifications to them will need to write a complete Pass to do that, which seems like a reasonable solution.

[vchuravy]

Okay I think I am done with this for now. I still want to add the general intrinsic op-out, but that is for the next major version.

[vchuravy]

Except that the tagging variant is broken. Grrml