Prepare juliainterface for GAP 4.15

[lgoettgens]

Alternative to most parts of #1239 (as discussed today with @fingolfin).

We should merge this PR asap, as the juliainterface code is now compatible with both gap 4.14 and 4.15. Therefore, the circular dependency mentioned in #1244 (comment) (point 6) should no longer be there.

I would suggest that we merge this, and then I will try to do all the rebuilds with this against the gap beta3 (which hopefully contains gap-system/gap#6124)

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 76.93%. Comparing base (97ce797) to head (0af5a09).
⚠️ Report is 4 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1248      +/-   ##
==========================================
+ Coverage   76.91%   76.93%   +0.02%     
==========================================
  Files          60       60              
  Lines        4778     4809      +31     
==========================================
+ Hits         3675     3700      +25     
- Misses       1103     1109       +6     

Files with missing lines	Coverage Δ
pkg/JuliaInterface/src/JuliaInterface.c	74.19% <ø> (ø)

... and 3 files with indirect coverage changes

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[fingolfin]

Huh, CI breaks -- a race condition? Maybe we need to protect the compilation of JuliaInterface against races with some kind of locking?

[fingolfin]

  1 dependency had output during precompilation:
┌ Oscar
│  [ Info: Compiling JuliaInterface ...
└  
     Testing Running tests...
[ Info: Compiling JuliaInterface ...

Adding worker processes
[ Info: /home/oscarci-tester/ssd-data/ssd-runner-02/_work/GAP.jl/GAP.jl/oscar-dev/Oscar/test/runtests.jl -- fixed SEED 42
      From worker 6:	[ Info: Compiling JuliaInterface ...
      From worker 5:	[ Info: Compiling JuliaInterface ...
      From worker 7:	[ Info: Compiling JuliaInterface ...
      From worker 4:	[ Info: Compiling JuliaInterface ...
      From worker 3:	[ Info: Compiling JuliaInterface ...
      From worker 2:	[ Info: Compiling JuliaInterface ...
      From worker 7:	/home/oscarci-tester/ssd-data/ssd-runner-02/_work/_tool/julia/1.10.10/x64/bin/julia: symbol lookup error: /home/oscarci-tester/ssd-data/ssd-runner-02/_work/GAP.jl/GAP.jl/pkg/JuliaInterface/bin/x86_64-pc-linux-gnu-julia1.10-64-kv9/JuliaInterface.so: undefined symbol: gap_julia
Worker 7 terminated.
Unhandled Task ERROR: EOFError: read end of file
Stacktrace:

So, yeah, it tries to compile JuliaInterface multiple times in parallel. A simple fix would be to use Pidfile.mkpidlock in build_JuliaInterface (resp. wrap the call to build_JuliaInterface in it).

(However that would still end up re-compiling JuliaInterface multiple times. To protect against that, more work is needed -- but perhaps it is not necessary given that this should not affect release versions of GAP.jl, so it's just for our internal use?

[lgoettgens]

Looks like an issue, but nothing new and not relevant to fix ASAP IMO