Fixup measurement for --trace-compile-timing w/ nested compilations. (#59363)
Use a separate inference_start and compilation_start, where
compilation_start does not do anything special for reentrancy.
Here is an example which has a quick-to-compile nested dynamic dispatch,
but that nested function runs for a long time:
```julia
./julia --startup=no --trace-compile=stderr --trace-compile-timing -e '
Base.@assume_effects :foldable function nested1(x)
sum(collect(x for _ in 1:1000_000_000))
end
f1(x) = nested1(sizeof(x)) + x
f1(2)'
#= 12.7 ms =# precompile(Tuple{typeof(Main.nested1), Int64})
#= 3809.3 ms =# precompile(Tuple{typeof(Main.f1), Int64})
```
This fixes a small issue introduced here:
https://github.com/JuliaLang/julia/pull/59220/files#r2292021838
julia
be59100b - Fixup measurement for --trace-compile-timing w/ nested compilations. (#59363)
