This commits adds a second FreeBSD 12 build job,
and splits the implementation of the FreeBSD module
into two modules, one for FreeBSD 11, and one for FreeBSD 12.
The FreeBSD 11 module is compiled always by default, and is
mostly forward compatible with FreeBSD 12 systems.
The FreeBSD 12 module is only built for now in libc's CI,
and uses FreeBSD 12 data types and APIs, linking to symbols
that are only available in FreeBSD 12.
Basically, when LIBC_CI env variable is defined, and the host
system is a FreeBSD 12 system, then the FreeBSD 12 module is
automatically built and tested. Conditional compilation is done
using a `cfg(freebsd12)` flag.
This commit also re-enables many tests, and documents why
some remain disabled.
This PR fixes the build on all platforms and all Rust version down to the
minimum Rust version supported by libc: Rust 1.13.0.
The `build.rs` is extended with logic to detect the newer Rust features used by
`libc` since Rust 1.13.0:
* Rust 1.19.0: `untagged_unions`. APIs using untagged unions are gated on
`cfg(libc_unions)` and not available on older Rust versions.
* Rust 1.25.0: `repr(align)`. Because `repr(align)` cannot be parsed by older
Rust versions, all uses of `repr(align)` are split into `align.rs` and
`no_align.rs` modules, which are gated on the `cfg(libc_align)` at the top
level. These modules sometimes contain macros that are expanded at the top
level to avoid privacy issues (`pub(crate)` is not available in older Rust
versions). Closes#1242 .
* Rust : `const` `mem::size_of`. These uses are worked around with hardcoded
constants on older Rust versions.
Also, `repr(packed)` structs cannot automatically `derive()` some traits like
`Debug`. These have been moved into `s_no_extra_traits!` and the lint of missing
`Debug` implementations on public items is silenced for these. We can manually
implement the `extra_traits` for these in a follow up PR. This is tracked
in #1243. Also, `extra_traits` does not enable `align` manually anymore.
Since `f64::to_bits` is not available in older Rust versions, its usage
has been replaced with a `transmute` to an `u64` which is what that method
does under the hood.
Closes#1232 .
