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

fusl/src/stdio/vsscanf.c

Index: fusl/src/stdio/vsscanf.c
diff --git a/fusl/src/stdio/vsscanf.c b/fusl/src/stdio/vsscanf.c
new file mode 100644
index 0000000000000000000000000000000000000000..929ffa3b0fd8a33754b0638536d0893bed74d9a1
--- /dev/null
+++ b/fusl/src/stdio/vsscanf.c
@@ -0,0 +1,18 @@
+#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);