change prepare worker to use fork instead of threads (#1685)

Co-authored-by: Marcin S <marcin@realemail.net>

polkadot/scripts/list-syscalls/prepare-worker-syscalls

@@ -16,6 +16,7 @@
 16 (ioctl)
 19 (readv)
 20 (writev)
+22 (pipe)
 24 (sched_yield)
 25 (mremap)
 28 (madvise)
@@ -25,7 +26,9 @@
 45 (recvfrom)
 46 (sendmsg)
 56 (clone)
+57 (fork)
 60 (exit)
+61 (wait4)
 62 (kill)
 72 (fcntl)
 79 (getcwd)
@@ -48,6 +51,7 @@
 158 (arch_prctl)
 165 (mount)
 166 (umount2)
+186 (gettid)
 200 (tkill)
 202 (futex)
 203 (sched_setaffinity)
@@ -62,6 +66,7 @@
 263 (unlinkat)
 272 (unshare)
 273 (set_robust_list)
+293 (pipe2)
 302 (prlimit64)
 309 (getcpu)
 318 (getrandom)