add all missing wchar functions except floating point parsers

these are mostly untested and adapted directly from corresponding byte
string functions and similar.

src/string/wcscasecmp.c

@@ -0,0 +1,7 @@
+#include <wchar.h>
+#include <wctype.h>
+
+int wcscasecmp(const wchar_t *l, const wchar_t *r)
+{
+	return wcsncasecmp(l, r, -1);
+}