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

fusl/src/stdio/vswscanf.c

Index: fusl/src/stdio/vswscanf.c
diff --git a/fusl/src/stdio/vswscanf.c b/fusl/src/stdio/vswscanf.c
new file mode 100644
index 0000000000000000000000000000000000000000..411dd39c9a27f763932126665cf95f9edc0bf422
--- /dev/null
+++ b/fusl/src/stdio/vswscanf.c
@@ -0,0 +1,39 @@
+#include "stdio_impl.h"
+#include "libc.h"
+#include <wchar.h>
+
+static size_t wstring_read(FILE *f, unsigned char *buf, size_t len)
+{
+	const wchar_t *src = f->cookie;
+	size_t k;
+
+	if (!src) return 0;
+
+	k = wcsrtombs((void *)f->buf, &src, f->buf_size, 0);
+	if (k==(size_t)-1) {
+		f->rpos = f->rend = 0;
+		return 0;
+	}
+
+	f->rpos = f->buf;
+	f->rend = f->buf + k;
+	f->cookie = (void *)src;
+
+	if (!len || !k) return 0;
+
+	*buf = *f->rpos++;
+	return 1;
+}
+
+int vswscanf(const wchar_t *restrict s, const wchar_t *restrict fmt, va_list ap)
+{
+	unsigned char buf[256];
+	FILE f = {
+		.buf = buf, .buf_size = sizeof buf,
+		.cookie = (void *)s,
+		.read = wstring_read, .lock = -1
+	};
+	return vfwscanf(&f, fmt, ap);
+}
+
+weak_alias(vswscanf,__isoc99_vswscanf);