libbb: introduce and use safe_waitpid (loops in EINTR)
*: use more approproate (shorter) versions of wait()

function                                             old     new   delta
safe_waitpid                                           -      48     +48
wait_any_nohang                                        -      17     +17
send_tree                                            365     369      +4
processorstop                                        432     435      +3
text_yank                                            110     108      -2
make_human_readable_str                              202     200      -2
crond_main                                          1368    1366      -2
handle_sigchld                                        49      43      -6
reapchild                                            166     159      -7
custom                                               260     250     -10
checkscript                                          191     177     -14
wait_nohang                                           17       -     -17
wait_pid                                              43       -     -43
------------------------------------------------------------------------------
(add/remove: 2/2 grow/shrink: 2/7 up/down: 72/-103)           Total: -31 bytes

diff --git a/runit/runsv.c b/runit/runsv.c
index 8c5a4d4..84f5193 100644
--- a/runit/runsv.c
+++ b/runit/runsv.c
@@ -282,8 +282,7 @@
 				execve(a, prog, environ);
 				fatal_cannot("run control/?");
 			}
-			while (wait_pid(&w, pid) == -1) {
-				if (errno == EINTR) continue;
+			while (safe_waitpid(pid, &w, 0) == -1) {
 				warn_cannot("wait for child control/?");
 				return 0;
 			}
@@ -593,7 +592,7 @@
 			int child;
 			int wstat;
 
-			child = wait_nohang(&wstat);
+			child = wait_any_nohang(&wstat);
 			if (!child)
 				break;
 			if ((child == -1) && (errno != EINTR))