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

fusl/src/unistd/pwritev.c

Index: fusl/src/unistd/pwritev.c
diff --git a/fusl/src/unistd/pwritev.c b/fusl/src/unistd/pwritev.c
new file mode 100644
index 0000000000000000000000000000000000000000..aec5d3235a0f45d4bf5b12c803afb67033a9e9b0
--- /dev/null
+++ b/fusl/src/unistd/pwritev.c
@@ -0,0 +1,13 @@
+#define _BSD_SOURCE
+#include <sys/uio.h>
+#include <unistd.h>
+#include "syscall.h"
+#include "libc.h"
+
+ssize_t pwritev(int fd, const struct iovec *iov, int count, off_t ofs)
+{
+	return syscall_cp(SYS_pwritev, fd, iov, count,
+		(long)(ofs), (long)(ofs>>32));
+}
+
+LFS64(pwritev);