kernel: remove environ arguments, remove sysenviron

[fingolfin]

This is an alternative to PR #3106 by @embray based on the discussion there.

Closes #3106

[embray]

Ah, thanks for taking care of this. It's fine by me; I will shed no tears if we just do away with the environ passing entirely.

[fingolfin]

I was motivated to do this because we just run into an issue with the GAPJulia bridge due to us being lazy and not passing the right environ value to libgap... fixing that would of course have been possible, but still rather annoying. So I took this as yet another sign that we should not pass environ via the API...

[embray]

Indeed: Most of the issues I've raised so far are in no way specific to Sage or even Python. The segfault we found could have happened to anyone using GAP_Initialize(). Whether or not it happens is mostly a matter of luck.

[dimpase]

Sure, no problem. I should have written tests to test environ passing, so now I'm glad I didn't (although this might have helped to locate the problem earlier...) Oh well.

[embray]

It just as easily might not have. This code path is already technically covered by the scant existing libgap tests. Like I said, whether or not this problem actually occurs depends on some very particular circumstances.

[sebasguts]

Looks good.

This also solves problems I had using homalg via Julia.

[codecov]

Codecov Report

Merging #3111 into master will increase coverage by 0.05%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #3111      +/-   ##
==========================================
+ Coverage   83.57%   83.62%   +0.05%     
==========================================
  Files         686      684       -2     
  Lines      336777   332055    -4722     
==========================================
- Hits       281462   277685    -3777     
+ Misses      55315    54370     -945

Impacted Files	Coverage Δ
src/sysfiles.c	43.54% <ø> (+2.95%)	⬆️
src/gap.c	83.03% <100%> (-0.28%)	⬇️
src/hpc/thread.c	56.91% <100%> (ø)	⬆️
src/libgap-api.c	21.92% <100%> (+1.76%)	⬆️
src/modules.h	33.33% <0%> (-66.67%)	⬇️
src/macfloat.h	20% <0%> (-51.43%)	⬇️
src/records.h	50% <0%> (-50%)	⬇️
src/gapstate.h	28.57% <0%> (-42.86%)	⬇️
src/gvars.h	66.66% <0%> (-33.34%)	⬇️
src/hookintrprtr.h	66.66% <0%> (-33.34%)	⬇️
... and 85 more

[codecov]

Codecov Report

Merging #3111 into master will decrease coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #3111      +/-   ##
==========================================
- Coverage   83.57%   83.57%   -0.01%     
==========================================
  Files         686      686              
  Lines      336777   336779       +2     
==========================================
- Hits       281462   281461       -1     
- Misses      55315    55318       +3

Impacted Files	Coverage Δ
src/sysfiles.c	40.59% <ø> (ø)	⬆️
src/gap.c	83.2% <100%> (-0.11%)	⬇️
src/hpc/thread.c	56.91% <100%> (ø)	⬆️
src/libgap-api.c	20.16% <100%> (ø)	⬆️
src/gapw95.c	100% <100%> (ø)	⬆️
src/sysmem.c	57.64% <0%> (-0.59%)	⬇️
src/objset.c	85.12% <0%> (-0.23%)	⬇️

[fingolfin]

Backported via 5867012