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

fusl/src/stdio/vsscanf.c

+#include "stdio_impl.h"
+#include "libc.h"
+
+static size_t do_read(FILE *f, unsigned char *buf, size_t len)
+{
+        return __string_read(f, buf, len);
+}
+
+int vsscanf(const char *restrict s, const char *restrict fmt, va_list ap)
+{
+        FILE f = {
+                .buf = (void *)s, .cookie = (void *)s,
+                .read = do_read, .lock = -1
+        };
+        return vfscanf(&f, fmt, ap);
+}
+
+weak_alias(vsscanf,__isoc99_vsscanf);