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

fusl/src/misc/lockf.c

+#include <unistd.h>
+#include <fcntl.h>
+#include <errno.h>
+#include "libc.h"
+
+int lockf(int fd, int op, off_t size)
+{
+        struct flock l = {
+                .l_type = F_WRLCK,
+                .l_whence = SEEK_CUR,
+                .l_len = size,
+        };
+        switch (op) {
+        case F_TEST:
+                l.l_type = F_RDLCK;
+                if (fcntl(fd, F_GETLK, &l) < 0)
+                        return -1;
+                if (l.l_type == F_UNLCK || l.l_pid == getpid())
+                        return 0;
+                errno = EACCES;
+                return -1;
+        case F_ULOCK:
+                l.l_type = F_UNLCK;
+        case F_TLOCK:
+                return fcntl(fd, F_SETLK, &l);
+        case F_LOCK:
+                return fcntl(fd, F_SETLKW, &l);
+        }
+        errno = EINVAL;
+        return -1;
+}
+
+LFS64(lockf);