lots of warnings in systest because of extern without ABI; ctest2 needs updating or replacing

[botovq]

building rust-openssl generates lots of warnings because ctest2 0.4.7 specified in systest/Cargo.toml is outdated:

warning: extern declarations without an explicit ABI are deprecated
     --> /tmp/rust-openssl/target/debug/build/systest-65324ffc3b624814/out/all.rs:51005:21
      |
51005 |                     extern {
      |                     ^^^^^^ help: explicitly specify the "C" ABI: `extern "C"`

warning: `systest` (bin "systest") generated 2633 warnings (run `cargo fix --bin "systest"` to apply 2633 suggestions)

Updating to the latest ctest2 version 0.4.10 fixes this, but now that ctest2 is no longer maintained, perhaps it's better to switch back to ctest?

JohnTitor/ctest2@8e352a0