add all missing wchar functions except floating point parsers

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

src/locale/wcscoll_l.c

@@ -0,0 +1,6 @@
+#include <wchar.h>
+
+int wcscoll_l(const wchar_t *l, const wchar_t *r, locale_t locale)
+{
+	return wcscoll(l, r);
+}

src/locale/wcsxfrm_l.c

@@ -0,0 +1,6 @@
+#include <wchar.h>
+
+size_t wcsxfrm_l(wchar_t *dest, const wchar_t *src, size_t n, locale_t locale)
+{
+	return wcsxfrm(dest, src, n);
+}