Skip max_align_t in FreeBSD10

This error was able to land because FreeBSD10 is not checked by bors yet (see: RCS PR: https://github.com/rust-lang/rust-central-station/pull/481) .

Fixes

Two patches fixing minor issues.

Add FreeBSD10 support

This adds libc-test support for Freebsd10 and a CI build job that tests
FreeBSD10 with LIBC_CI only.

cc @asomers this is a follow up to #1491 .

Implement max_align_t

Implement `max_align_t` for windows and unix targets.

WIP: at this stage I just want to see what breaks.

pthread_exit return type fix

Closes: #1520

Re-enable all roundtrip tests

Signed-off-by: Philipp Gesang <phg@phi-gamma.net>

It's *msg_prio* in both manpages and posix.

Fix building error at backtrace

I get this error when builind backtrace:

error[E0308]: mismatched types
  --> /folk/prj-rust-dev/bpang/ala-diab-pb19l/fix_bugs/latest/.cargo/git/checkouts/backtrace-rs-fb1f822361417489/e745627/src/symboli\
ze/dladdr.rs:38:73
   |
38 |                         Some(SymbolName::new(slice::from_raw_parts(ptr, len)))
   |                                                                         ^^^ expected usize, found u64
help: you can convert an `u64` to `usize` and panic if the converted value wouldn't fit

It shows the 'size_t' is expected to be defined as "usize".

defining uintptr_t = usize and intptr_t/ptrdiff_t = isize, and using uintptr_t to define size_t, and intptr_t to define ssize_t.

Sync with rust-lang/libc branch master

updates for vxworks

fix problems found in testing
VxWorks socket and epoll definitions needed by mio and related crates; epoll only supported in VxWorks kernel; just provide stub definitions for user mode for now
Fixed usage of isize
libc VxWorks cleanups and additions
remove copyright notice

2. implement Debug for big size array
3. remove code related to epoll
4. use 'pub enum' for _Vx_semaphore

This adds libc-test support for Freebsd10 and a CI build job that tests
FreeBSD10 with LIBC_CI only.

add isblank

Fixes #1509

Add SCHED_RESET_ON_FORK

This is a fix for #1511, and is valid for musl and glibc.

Test FreeBSD 12 on latest nightly

~~Let's see if [libc update](https://github.com/rust-lang/rust/pull/63806) for Rust fixed it.~~

Fixes https://github.com/rust-lang/libc/issues/1489

freebsdlike: add several utmpx constants

This adds several `utmpx.h` constants for FreeBSD and DragonflyBSD.

Ref: https://github.com/freebsd/freebsd/blob/a1d2b5187332a366a897689c5fb41d38d7e1b0d8/include/utmpx.h
Ref: http://gitweb.dragonflybsd.org/dragonfly.git/blob/HEAD:/include/utmpx.h

Workaround Azure images not supporting rustup self update

Copy structs from bits/user.h for musl x86_64

While statically compiling a binary with `musl`, I ran into the following error regarding a missing struct:

```
error[E0412]: cannot find type `user_regs_struct` in crate `libc`
  --> src/debug.rs:37:32
   |
37 | fn show_user_regs(regs: &libc::user_regs_struct) -> String {
   |                                ^^^^^^^^^^^^^^^^ not found in `libc`
```

This struct was previously added for `glibc` in #599, but was never added to `musl`, despite the data format being the same in both.

This fix simply copies `user_regs_struct` into the proper location within the `musl` files.