Fix Pkg.precompile ext races

[IanButterworth]

If I force this to @info
https://github.com/JuliaLang/julia/blob/8cacc1c7320ac8092625b4dd2e4b96b55c14d9d3/base/loading.jl#L3069

On master I get

(@v1.11) pkg> precompile
Precompiling project...
  169 dependencies successfully precompiled in 98 seconds. 35 already precompiled.
  2 dependencies had output during precompilation:
┌ ChainRulesCore
│  ┌ Info: Waiting for another process (pid: 41643) to finish precompiling CompatLinearAlgebraExt [dbe5ba0b-aecc-598a-a867-79051b540f49]
│  └ @ Base loading.jl:3071
└  
┌ Distances → DistancesChainRulesCoreExt
│  ┌ Info: Waiting for another process (pid: 41643) to finish precompiling DistancesSparseArraysExt [feee1041-5e3e-5b48-b2f8-f25e4435f184]
│  └ @ Base loading.jl:3071
└  

which indicates that there is race that's being limited by the cache pidlocks.

If a package has multiple active extensions Pkg.precompile wasn't sequencing the extensions meaning they raced to precompile.

So, with this PR

(@v1.11) pkg> precompile
Precompiling project...
  169 dependencies successfully precompiled in 102 seconds. 35 already precompiled.
  1 dependency had output during precompilation:
┌ ChainRulesCore
│  ┌ Info: Waiting for another process (pid: 49287) to finish precompiling CompatLinearAlgebraExt [dbe5ba0b-aecc-598a-a867-79051b540f49]
│  └ @ Base loading.jl:3071
└  

I'm looking into the ChainRulesCore -> CompatLinearAlgebraExt issue too.

[IanButterworth]

Ok, after that 2nd commit I now get no warnings.

Turns out the extension dependency insertion loop needed to run after the full depsmap had been built, otherwise it wasn't aware of the full environment. (Duh)

By the way, the state management in Pkg.precompile has become a mess. I fully intend on tidying it up, but I think I will do it after moving it to Base, as doing both tasks at the same time has tripped up my efforts to get that done a couple of times already.

[KristofferC]

I haven't gone through the logic but the logging output seems to confirm it works so 👍