wip/kefir 0.5.0 NetBSD

Kefir is an independent compiler for the C17/C23 programming language, developed by Jevgenij Protopopov. Kefir has been validated with a test suite of 80 software projects, among which are GNU core- and binutils, Curl, Nginx, OpenSSL, Perl, Postgresql, Tcl and many others. The compiler targets x86_64 architecture and System-V AMD64 ABI, supporting Linux, FreeBSD, NetBSD and OpenBSD. While the primary priority is compatibility and compliance, Kefir also features conservative SSA-based optimization pipeline, debug information generation, position-independent code, and implements bit-identical bootstrap. Kefir focuses on C source code translation to assembly, and integrates with the rest of system toolchain (assembler, linker, standard library) for other tasks.