Improve haiku support

[GrayJack]

• Make (current) all tools pass check on haiku
• Improvements on core

[GrayJack]

bors r+

[bors[bot]]

Build succeeded:

• Format
• FreeBSD (1.46.0)
• FreeBSD (stable)
• Fuchsia (1.46.0)
• Fuchsia (stable)
• Illumos (1.47.0)
• Illumos (stable)
• Linux (1.46.0)
• Linux (stable)
• MacOS (1.46.0)
• MacOS (stable)
• NetBSD (1.46.0)
• NetBSD (stable)
• Solaris (1.46.0)
• Solaris (stable)