syscalls: refactor vfork02 using new API #1609

Job	Run time
job (debian:oldstable, gcc)	6m 55s
job (debian:oldstable, clang)	11m 22s
job (debian:stable, gcc, out, minimal)	8m 13s
job (debian:stable, arm64, aarch64-linux-gnu-gcc, 1, out, cross-compile)	4m 15s
job (fedora:latest, clang, 1)	11m 10s
job (debian:stable, gcc, i386)	8m 51s
job (debian:stable, s390x, s390x-linux-gnu-gcc, 1, out, cross-compile)	3m 36s
job (debian:testing, gcc)	5m 9s
job (debian:stable, ppc64el, powerpc64le-linux-gnu-gcc, 1, out, cross-compile)	3m 58s
job (alpine:latest, gcc)	9m 23s
job (quay.io/centos/centos:stream9, gcc, out)	3m 18s
job (opensuse/archive:42.2, gcc)	8m 20s
job (opensuse/leap:latest, gcc)	8m 51s
job (ubuntu:bionic, gcc)	9m 6s
job (debian:testing, clang)	10m 28s
job (ubuntu:jammy, gcc, out)	8m 39s
	2h 1m 34s

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