Unexport catch_stack

[c42f]

This API is experimental in julia 1.1 and will be replaced with
something more convenient (see #29901). In the meantime, make sure it's
clearly marked as experimental and not exported from Base.

[c42f]

I've got a weird error building the docs locally which I haven't had time to resolve yet (hence the annoying CI breakage, hopefully fixed now). Logs in case you guys have some idea:

chris@xyz:~/dev/julia/doc$ make VERBOSE=1
/home/chris/dev/julia/deps/tools/jlchecksum UnicodeData.txt
Building HTML documentation.
/home/chris/dev/julia/usr/bin/julia --color=yes /home/chris/dev/julia/doc/make.jl linkcheck= doctest= buildroot=/home/chris/dev/julia
  Updating registry at `~/dev/julia/doc/deps/registries/General`
  Updating git-repo `https://github.com/JuliaRegistries/General.git`
ERROR: LoadError: ArgumentError: Package Pkg-193e494c22f7ce8b5956829286c6212133edcbf1 not found in current path:
- Run `import Pkg; Pkg.add("Pkg-193e494c22f7ce8b5956829286c6212133edcbf1")` to install the Pkg-193e494c22f7ce8b5956829286c6212133edcbf1 package.

[KristofferC]

Delete usr folder and rebuild.

[c42f]

CI error on win32 is #29880