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

fusl/src/stdio/vdprintf.c

Index: fusl/src/stdio/vdprintf.c
diff --git a/fusl/src/stdio/vdprintf.c b/fusl/src/stdio/vdprintf.c
new file mode 100644
index 0000000000000000000000000000000000000000..c35d9b4fb0412fdefb2f4a07c198b8de8b451871
--- /dev/null
+++ b/fusl/src/stdio/vdprintf.c
@@ -0,0 +1,16 @@
+#include "stdio_impl.h"
+
+static size_t wrap_write(FILE *f, const unsigned char *buf, size_t len)
+{
+	return __stdio_write(f, buf, len);
+}
+
+int vdprintf(int fd, const char *restrict fmt, va_list ap)
+{
+	FILE f = {
+		.fd = fd, .lbf = EOF, .write = wrap_write,
+		.buf = (void *)fmt, .buf_size = 0,
+		.lock = -1
+	};
+	return vfprintf(&f, fmt, ap);
+}