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

fusl/src/stdio/vdprintf.c

+#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);
+}