Adapt handling of world ages to upstream changes

[maleadt]

Adapts to JuliaLang/julia#48611.
Helps towards #146, but doesn't fix it yet.
Ref #394

[codecov]

Codecov Report

Patch coverage: 85.05% and project coverage change: +1.55 🎉

Comparison is base (7e0a6ff) 78.74% compared to head (6be6ee6) 80.29%.

❗ Current head 6be6ee6 differs from pull request most recent head 33728eb. Consider uploading reports for the commit 33728eb to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #403      +/-   ##
==========================================
+ Coverage   78.74%   80.29%   +1.55%     
==========================================
  Files          24       24              
  Lines        2856     2888      +32     
==========================================
+ Hits         2249     2319      +70     
+ Misses        607      569      -38     

Impacted Files	Coverage Δ
src/jlgen.jl	80.62% <80.86%> (+8.60%)	⬆️
src/reflection.jl	36.43% <83.33%> (+1.04%)	⬆️
src/driver.jl	92.09% <84.00%> (+0.63%)	⬆️
src/irgen.jl	87.97% <95.45%> (+1.51%)	⬆️
src/cache.jl	96.15% <100.00%> (+3.96%)	⬆️
src/interface.jl	80.95% <100.00%> (+3.17%)	⬆️
src/rtlib.jl	96.20% <100.00%> (ø)
src/validation.jl	97.33% <100.00%> (+4.00%)	⬆️

... and 3 files with indirect coverage changes

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[oscardssmith]

Should this be merged? GPUCompiler is failing on julia nightly due to the lack of this.

[maleadt]

I'm still working in some improvements, but I'll be sure to merge and tag this today to unblock that part of the stack.