[llvm] [LLVM] [Support] Query the terminal width using the termios API (PR #143514)

[via llvm-commits]

Sirraide wrote:

> LLVM Buildbot has detected a new failure on builder `clang-solaris11-sparcv9` running on `solaris11-sparcv9` while building `llvm` at step 4 "build stage 1".

This one looks like an actual failure:
```
/opt/llvm-buildbot/home/solaris11-sparcv9/clang-solaris11-sparcv9/llvm/llvm/lib/Support/Unix/Process.inc:324:18: error: variable has incomplete type 'struct winsize'
  324 |   struct winsize ws;
      |                  ^
```

https://github.com/llvm/llvm-project/pull/143514