freebsd: Use compiler.h from FreeBSD's base's linuxkpi

[bsdimp]

The FreeBSD linux/compiler.h in OpenZFS was copied from a very old version of FreeBSD's linuxkpi's linux/compiler.h. There's no need for this duplication. Use FreeBSD's linuxkpi version instead, and provide zfs_fallthrough to augment it (it's all that's needed). Use #pragma once to avoid naming issues for guard variables. Since this is a complete rewrite, use my copyright here (the original code in FreeBSD still credits everybody). This works back at least to FreeBSD 12.4, which is not out of support, and all newer releases.

Remove extra copies of macros that were defined elsewhere, but are now properly defined in LinuxKPI so are redundant.

Sponsored-by: Netflix
Signed-off-by: Warner Losh imp@bsdimp.com

Motivation and Context

Description

OpenZFS has an ancient copy of FreeBSD's LKPI compiler.h. Rather than make yet another copy in an indirect tree that has to be maintained, make the OpenZFS one use FreeBSD's directly. Since at least FreeBSD 12, this has everything needed except zfs_fallthrough, so define that here.

How Has This Been Tested?

Ran FreeBSD's make universe with these changes on FreeBSD main. I ran make buildworld and buildkernel on aarch64 and amd64 for stable/14, stable/13 and stable/12. I booted the result on main with a fresh world and observed no regressions.

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.
• [NA] I have updated the documentation accordingly.
• I have read the contributing document.
• [NA] I have added tests to cover my changes.
• I have run the ZFS Test Suite with this change applied. (earlier freebsd version)
• All commit messages are properly formatted and contain Signed-off-by.