Unbreak FreeBSD cross-build on MacOS broken in 051460b8b

[mmatuska]

Motivation and Context

Fix FreeBSD cross-build on MacOS broken in 051460b
Minimizing code diff between OpenZFS and FreeBSD

Description

MacOS used FreeBSD-compatible getprogname() and pthread_getname_np(). But pthread_getthreadid_np() does not exist on MacOS. This implements libspl_gettid() using pthread_threadid_np() to get the thread id of the current thread.

How Has This Been Tested?

Tested with FreeBSD GitHub actions
freebsd/freebsd-src@3c1be0b
https://github.com/freebsd/freebsd-src/actions/runs/8946387771/job/24576944970
https://github.com/freebsd/freebsd-src/actions/runs/8946387771/job/24576945408

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Performance enhancement (non-breaking change which improves efficiency)
• Code cleanup (non-breaking change which makes code smaller or more readable)
• Breaking change (fix or feature that would cause existing functionality to change)
• Library ABI change (libzfs, libzfs_core, libnvpair, libuutil and libzfsbootenv)
• Documentation (a change to man pages or other documentation)

Checklist:

• My code follows the OpenZFS code style requirements.
• I have updated the documentation accordingly.
• I have read the contributing document.
• I have added tests to cover my changes.
• I have run the ZFS Test Suite with this change applied.
• All commit messages are properly formatted and contain Signed-off-by.

[mmatuska]

@robn if you have a better solution, I am of course open for it

[robn]

Interesting. If this gets things moving, I'm ok with it, so approved.

I'm interested in what you're actually doing though. Are you compiling for FreeBSD on macOS? "cross-build" sounds like yes, but if that's true, I don't understand why __APPLE__ would be defined if you're targetting FreeBSD userspace. But maybe you're compiling FreeBSD userspace on macOS for macOS, and macOS defines __FreeBSD__ as well? Or, something else entirely?

It won't make a difference to this PR, but it might change how I approach a couple of things in the future if __FreeBSD__ is not enough of an indicator of a platform target.

[mmatuska]

Interesting. If this gets things moving, I'm ok with it, so approved.

I'm interested in what you're actually doing though. Are you compiling for FreeBSD on macOS? "cross-build" sounds like yes, but if that's true, I don't understand why __APPLE__ would be defined if you're targetting FreeBSD userspace. But maybe you're compiling FreeBSD userspace on macOS for macOS, and macOS defines __FreeBSD__ as well? Or, something else entirely?

It won't make a difference to this PR, but it might change how I approach a couple of things in the future if __FreeBSD__ is not enough of an indicator of a platform target.

The kernel-toolchain is compiled as MacOS binaries and libspl is part of it.