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

fusl/src/string/wcsncasecmp.c

Index: fusl/src/string/wcsncasecmp.c
diff --git a/fusl/src/string/wcsncasecmp.c b/fusl/src/string/wcsncasecmp.c
new file mode 100644
index 0000000000000000000000000000000000000000..8fefe799c4370312f7539cc7a2e24016d9b7f546
--- /dev/null
+++ b/fusl/src/string/wcsncasecmp.c
@@ -0,0 +1,9 @@
+#include <wchar.h>
+#include <wctype.h>
+
+int wcsncasecmp(const wchar_t *l, const wchar_t *r, size_t n)
+{
+	if (!n--) return 0;
+	for (; *l && *r && n && (*l == *r || towlower(*l) == towlower(*r)); l++, r++, n--);
+	return towlower(*l) - towlower(*r);
+}