This patch is part of a series that adds origin-tracking to the debugify
source location coverage checks, allowing us to report symbolized stack
traces of the point where missing source locations appear.

This patch adds a pair of new functions in `signals.h` that can be used
to collect and symbolize stack traces respectively. This has major
implementation overlap with the existing stack trace
collection/symbolizing methods, but the existing functions are
specialized for dumping a stack trace to stderr when LLVM crashes, while
these new functions are meant to be called repeatedly during the
execution of the program, and therefore we need a separate set of
functions.

Cygwin environment has pthread functionality but LLVM integration
doesn't care it nor provide fallback.
Using Linux integration for Cygwin works fine.

#143514 broke the `clang-solaris11-sparcv9` bot; from what I can tell
that’s Solaris and according to `SolarisTargetInfo::getOSDefines`, the
macro `__sun__` should be defined on Solaris, so check for that and
don’t try to query the terminal size if it is defined.

Not sure this is the best solution but hopefully it fixes the bot.

On unix systems, we were trying to determine the terminal width using
the `COULMNS` environment variable. Unfortunately, `COLUMNS` is not 
exported by all shells and thus not available on some systems.

We were previously using `ioctl()` for this; fall back to doing so if `COLUMNS`
does not exist or does not store a positive integer.

This essentially reverts a3eb3d3d92d037fe3c9deaad87f6fc42fe9ea766 and
parts of https://reviews.llvm.org/D61326.

For more information, see #139499.

Fixes #139499.

This patch removes the C++
disablezOSAutoConversion,enablezOSAutoConversion declarations and also
updates Path.inc to use the common function.

In Unix/DynamicLibrary.inc, it was already known that Cygwin required
use of `RTLD_DEFAULT` as the `Handle` parameter to `DLSym` to search all
modules for a symbol. Unfortunately, RTLD_DEFAULT is defined as NULL, so
the existing checks of the `Process` handle meant `DLSym` would never be
called on Cygwin. Use the existing `&Invalid` sentinel instead of
`nullptr` for the `Process` handle.

This commit resolves a potential issue of working with uninitialized
memory when querying the CPU's affinity. The man page of
`sched_getaffinity` does not guarantee that the memory will be fully
overwritten, so this change should ensure that issues are avoided.

This PR is in reference to porting LLDB on AIX.
Link to discussions on llvm discourse and github:

1. https://discourse.llvm.org/t/port-lldb-to-ibm-aix/80640
2. https://github.com/llvm/llvm-project/issues/101657
The complete changes for porting are present in this draft PR:
https://github.com/llvm/llvm-project/pull/102601

- Added changes to getProcFile() with threadID, including testcase for
AIX.
- Added support for AIX to get_threadid() from llvm.

This PR is part of a series to upstream managarm support, as laid out in
the
[RFC](https://discourse.llvm.org/t/rfc-new-proposed-managarm-support-for-llvm-and-clang-87845/85884/1).
This PR is a follow-up to #87845.

The intention here is to add the managarm target to the LLVM support
lib, in preparation for a follow-up that would add the missing clang
driver bits.