Need `--cfg=libc_align` in v0.3.16 but not v0.3.15; why? about socket2

[wchargin]

Ah! Thank you, thank you. Indeed, it can parse cfg=... outputs from
build.rs, but only if you specify gen_buildrs = true (by design, to
make it explicit where the build isn’t necessarily hermetic), and
I hadn’t done so for this crate. Silly of me; sorry for the trouble, and
thanks for the pointer. :-)

[Thomasdezeeuw]

This was done in #120, maybe @faern can elaborate why it's needed a bit.

[faern]

It is very strange that you get this on rustc 1.47.0. According to the libc build script it should automatically activate libc_align when you compile it on rustc 1.25 or newer: https://github.com/rust-lang/libc/blob/master/build.rs#L56-L59

And also having socket2 activate the feature should also make the need for the __align field go away.

I have never used Bazel. Maybe it does not support features or build scripts enough?

[faern]

Or maybe it simply does not parse the build script output of cargo:rustc-cfg=libc_align!? That would make kind of sense since the line includes cargo:. But then again, would not almost everything break if it did not support those? :O