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

fusl/src/string/wcscspn.c

Index: fusl/src/string/wcscspn.c
diff --git a/fusl/src/string/wcscspn.c b/fusl/src/string/wcscspn.c
new file mode 100644
index 0000000000000000000000000000000000000000..c4e52722e11d8d5cccb862a95a93dab2564dcc6a
--- /dev/null
+++ b/fusl/src/string/wcscspn.c
@@ -0,0 +1,10 @@
+#include <wchar.h>
+
+size_t wcscspn(const wchar_t *s, const wchar_t *c)
+{
+	const wchar_t *a;
+	if (!c[0]) return wcslen(s);
+	if (!c[1]) return (s=wcschr(a=s, *c)) ? s-a : wcslen(a);
+	for (a=s; *s && !wcschr(c, *s); s++);
+	return s-a;
+}