Replace references of static externs to addr_of!. We need to do this …

[safinaskar]

…because of rust-lang/rust#114447 .

I need this, because I plan to send PR to crate libc, which will add environ static extern for UNIX. Unfortunately, environ generates annoying warning during testing due to rust-lang/rust#114447 , so I'm sending this PR to ctest2 first.

I tested this ctest2 PR with my fork of crate libc, which adds environ, and all works great.

Also, even if you opposed to proposed crate libc change, this ctest2 PR is of general usefulness anyway.

Also, this ctest2 PR always unconditionally generates addr_of! invocation. This is okay, because ctest2's MSRV is 1.56.0, and addr_of! was added in 1.51.0.

Please, make ctest2 release after this PR is applied

[safinaskar]

CI is failing. But I think this is not because of this PR. If you want, I can try to fix CI anyway

[safinaskar]

@JohnTitor , I fixed CI!!!

I added two commits (second and third), and now CI works. First commit (i. e. introducing addr_of!) is needed for CI, too. So, all 3 commits are needed for CI. Please, review and apply this PR

[JohnTitor]

Thanks!