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

fusl/src/linux/ptrace.c

+#include <sys/ptrace.h>
+#include <stdarg.h>
+#include <unistd.h>
+#include "syscall.h"
+
+long ptrace(int req, ...)
+{
+        va_list ap;
+        pid_t pid;
+        void *addr, *data, *addr2;
+        long ret, result;
+
+        va_start(ap, req);
+        pid = va_arg(ap, pid_t);
+        addr = va_arg(ap, void *);
+        data = va_arg(ap, void *);
+        addr2 = va_arg(ap, void *);
+        va_end(ap);
+
+        if (req-1U < 3) data = &result;
+        ret = syscall(SYS_ptrace, req, pid, addr, data, addr2);
+
+        if (ret < 0 || req-1U >= 3) return ret;
+        return result;
+}