Add a no-clone3 feature to disable clone3

[jprendes]

This PR adds a no-clone3 feature that disables the use of clone3 in libcontainer.

This can be used to counteract the undefined behaviour introduced by using a raw sysall for clone3, which leads to problem in musl and on glibc when the main process uses threads.

See containerd/runwasi#347

[YJDoc2]

Hey, actually I was also trying the same here #2418 which either takes clone3 or clone depending on feature without any fallback. Its failing some tests, so need to see that there.

[codecov-commenter]

Codecov Report

Merging #2419 (dd324aa) into main (b968ac5) will decrease coverage by 0.01%.
The diff coverage is 100.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2419      +/-   ##
==========================================
- Coverage   66.01%   66.01%   -0.01%     
==========================================
  Files         133      133              
  Lines       16832    16822      -10     
==========================================
- Hits        11112    11105       -7     
+ Misses       5720     5717       -3     

[YJDoc2]

Hey, there's one conflict due to recent merge in master, can you rebase? Also I saw your comment on my PR regarding failing test, I'll try to get to that, or if this is done first/ has more preferable approach, we can go ahead with this.

Also a nit, personal preference : can the feature name be "positive" i.e. instead of no-clone3 , can we have clone3, and invert the checks instead?

[jprendes]

can the feature name be "positive" i.e. instead of no-clone3 , can we have clone3, and invert the checks instead?

I thought about that and my concern is that when we request no-clone3, we really don't want clone3 (since we know we are hitting undefined behaviour somewhere).
Due to how cargo resolves features (the union of all features requested), a feature can be enabled by another crate even if your crate didn't enable it. The same doesn't apply to disabling features (you can't disable features other than default).
Naming it clone3 means that some other crate can accidentally enable it.
Naming it no-clone3 means that once we enable it, it can't be accidentally disabled.

[jprendes]

can you rebase?

Rebased :-)

[jprendes]

Converting to draft as this doesn't fix the sporadic failures in containerd/runwasi#347

[utam0k]

@jprendes Can we close this PR?