Add ucontext_t and {get,set,make,swap}context for powerpc64-linux (cont.)

[xingxue-ibm]

Description

This continues the PR Add ucontext_t and {get,set,make,swap}context for powerpc64-linux for adding ucontext_t, mcontext_t, and related structures and functions.

Relevant header files:
ucontext_t and mcontext_t - https://github.com/bminor/glibc/blob/a6eb8285d9bfb7ec0875b85ca356e833ff964d4f/sysdeps/unix/sysv/linux/powerpc/sys/ucontext.h#L155-L196
pt_regs - https://github.com/torvalds/linux/blob/master/arch/powerpc/include/uapi/asm/ptrace.h
clone_args - https://github.com/torvalds/linux/blob/f83ec76bf285bea5727f478a68b894f5543ca76e/include/uapi/linux/sched.h#L92
{get,set,make,swap}context - https://github.com/bminor/glibc/blob/a6eb8285d9bfb7ec0875b85ca356e833ff964d4f/stdlib/ucontext.h#L34-L52

Closes: #3986

Sources

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

The test failed with the following errors, which do not seem to be related to the changes in this PR.

  error: expected `*` or `+`
     --> /home/xingxue/libc/target/powerpc64le-unknown-linux-gnu/debug/build/libc-test-7e8f2ce60f339395/out/src-hotfix/macros.rs:228:9
      |
  228 |         pub enum $ty_name:ident {
      |         ^^^

  error: expected `*` or `+`
     --> /home/xingxue/libc/target/powerpc64le-unknown-linux-gnu/debug/build/libc-test-7e8f2ce60f339395/out/src-hotfix/macros.rs:229:47
      |
  229 |             $($variant:ident $(= $value:expr)?,)+
      |                                               ^

  error: expected `*` or `+`
     --> /home/xingxue/libc/target/powerpc64le-unknown-linux-gnu/debug/build/libc-test-7e8f2ce60f339395/out/src-hotfix/macros.rs:242:9
      |
  242 |         pub enum $ty_name:ident {
      |         ^^^

  error: expected `*` or `+`
     --> /home/xingxue/libc/target/powerpc64le-unknown-linux-gnu/debug/build/libc-test-7e8f2ce60f339395/out/src-hotfix/macros.rs:243:47
      |
  243 |             $($variant:ident $(= $value:expr)?,)+
      |                                               ^
    ....

[tgross35]

Looks great, thank you for getting this over the line!

The error looks like something from the old ctest that we recently replaced, so hopefully it should go away with a rebase.

[tgross35]

It looks like the new ctest doesn't like type aliases to arrays. You can ignore the type for now in libc-test/build.rs, otherwise I'll try to figure out how to fix things. (Cc @mbyx)

[mbyx]

According to the docs for skip_roundtrip, aliases to arrays have to manually be skipped. It should be possible to automate that behaviour however. I'll try to make a PR when I have time.