Add a "fork" of musl as //fusl.

fusl/src/process/system.c

+#include <unistd.h>
+#include <stdlib.h>
+#include <signal.h>
+#include <sys/wait.h>
+#include <spawn.h>
+#include <errno.h>
+#include "pthread_impl.h"
+#include "libc.h"
+
+extern char **__environ;
+
+int system(const char *cmd)
+{
+        pid_t pid;
+        sigset_t old, reset;
+        struct sigaction sa = { .sa_handler = SIG_IGN }, oldint, oldquit;
+        int status = 0x7f00, ret;
+        posix_spawnattr_t attr;
+
+        pthread_testcancel();
+
+        if (!cmd) return 1;
+
+        sigaction(SIGINT, &sa, &oldint);
+        sigaction(SIGQUIT, &sa, &oldquit);
+        sigaddset(&sa.sa_mask, SIGCHLD);
+        sigprocmask(SIG_BLOCK, &sa.sa_mask, &old);
+
+        sigemptyset(&reset);
+        if (oldint.sa_handler != SIG_IGN) sigaddset(&reset, SIGINT);
+        if (oldquit.sa_handler != SIG_IGN) sigaddset(&reset, SIGQUIT);
+        posix_spawnattr_init(&attr);
+        posix_spawnattr_setsigmask(&attr, &old);
+        posix_spawnattr_setsigdefault(&attr, &reset);
+        posix_spawnattr_setflags(&attr, POSIX_SPAWN_SETSIGDEF|POSIX_SPAWN_SETSIGMASK);
+        ret = posix_spawn(&pid, "/bin/sh", 0, &attr,
+                (char *[]){"sh", "-c", (char *)cmd, 0}, __environ);
+        posix_spawnattr_destroy(&attr);
+
+        if (!ret) while (waitpid(pid, &status, 0)<0 && errno == EINTR);
+        sigaction(SIGINT, &oldint, NULL);
+        sigaction(SIGQUIT, &oldquit, NULL);
+        sigprocmask(SIG_SETMASK, &old, NULL);
+
+        if (ret) errno = ret;
+        return status;
+}