Remove termios2 from musl targets

[Susurrus]

This wasn't caught because the tests disable checking for termios2 on all targets, so I enabled it on musl targets to prevent this from recurring.

Closes #1006

[rust-highfive]

r? @alexcrichton

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[alexcrichton]

Has this been published? If so I think this'd be a breaking change?

If so, do we know as well how this passed ctest without being caught?

[Susurrus]

Has this been published? If so I think this'd be a breaking change?

Yes it has. musl targets are all Tier-2 or worse targets, so it depends on how big of a problem it is to break things on these platforms. Though this is a bug fix. I think it'd be very useful as a contributor to have the breaking changes policy addressed in the README or CONTRIBUTOR documentation to address this.

If so, do we know as well how this passed ctest without being caught?

I'll need to dig into this a bit more. Looking at the testing, termios2 is excluded from the regular test because of import conflicts with the C headers. So it's tested as part of the second fcntl tests. termios2 is the only struct checked on non-musl platforms, but for musl targets, I'd expect that it gets checked. The relevant code is:

        if !musl {
            cfg.skip_struct(|s| {
                s != "termios2"
            });
        }

[alexcrichton]

Oh dear, that sounds bad! Currently we don't ever remove APIs from libc, so perhaps these could be marked as deprecated with a message saying that they were added mistakenly and are guaranteed to not work on musl?

[Susurrus]

Merged into #629 so closing this.