POSIX: change struct stat/stat64 times to timespec

[xbjfk]

Description

Since this was evidently a problem when doing musl changes,no objections in #4965 and v1 being in alpha, it's time to rip the band aid off and do it.

Of course, there are a couple unsolved questions:

• Windows doesn't have the _nsec fields:

  libc/src/windows/mod.rs

  Lines 52 to 54 in 17adf2d

  	pub st_atime: time64_t,
  	pub st_mtime: time64_t,
  	pub st_ctime: time64_t,

  There is also a note that should probably be addressed before 1.0:

  libc/src/windows/mod.rs

  Line 43 in 17adf2d

  pub struct stat {

• Newlib has padding where the nsecs should be:

  libc/src/unix/newlib/generic.rs

  Lines 22 to 27 in 0dddfc8

  	pub st_atime: crate::time_t,
  	pub st_spare1: c_long,
  	pub st_mtime: crate::time_t,
  	pub st_spare2: c_long,
  	pub st_ctime: crate::time_t,
  	pub st_spare3: c_long,

  But upstream uses timespec for some architectures: https://github.com/cygwin/cygwin/blob/a0ccec7e7a16b01037ece1947610f768ab7f081a/newlib/libc/include/sys/stat.h#L37-L59
• I don't know what is going on with Apple - they use xtimespec instead of xtim: https://github.com/apple-oss-distributions/xnu/blob/f6217f891ac0bb64f3d375211650a4c1ff8ca1ea/bsd/sys/stat.h#L202-L206 - but interestingly, Swift seems to rename this to the POSIX correct form, despite the underlying C headers not having it: https://github.com/apple/swift-system/blob/main/Sources/System/FileSystem/Stat.swift#L428. We need to pick one.

Also, solid and qurt do not have nsec at all. NTO and VxWorks have already migrated.

Sources

In each relevant commit.

Checklist

• Relevant tests in libc-test/semver have been updated
• No placeholder or unstable values like *LAST or *MAX are
  included (see #3131)
• Tested locally (cd libc-test && cargo test --target mytarget);
  especially relevant for platforms that may not be checked in CI

As discussed in / Fixes: #4965

[rustbot]

Some changes occurred in a solarish module

cc @jclulow, @pfmooney

Some changes occurred in an Android module

cc @maurer

Some changes occurred in an OpenBSD module

cc @semarie

Some changes occurred in a NetBSD-like module

cc @semarie

[xbjfk]

Hmm, since freebsd11 no longer depends on c_long, the prelude is no longer necessary - but it feels wrong to remove.