Adjusted mingw libxml2 build to exclude libiconv

In libxml2 2.13.6 and previous the configure script would allow no iconv to be found.
With 2.14.1 the configure script was changed to default to looking for iconv if no explicit --without-iconv was specified.

We have been building libxml2 on mingw platform without iconv "always" as far as I can tell so this is not a functional change, only a build-time change.

Ticket: ENT-12744
Changelog: none

Author: craigcomstock

deps-packaging/libxml2/mingw/debian/rules

@@ -12,7 +12,8 @@ build: build-stamp
 build-stamp:
 	dh_testdir
 
-	./configure --host=$(DEB_HOST_GNU_TYPE) --prefix=$(PREFIX) --without-python
+	# ENT-12744 note: --without-iconv is needed on ubuntu-16 build host, we can use win-iconv-mingw-w64-dev on ubuntu-20+ when we get there.
+	./configure --host=$(DEB_HOST_GNU_TYPE) --prefix=$(PREFIX) --without-python --without-iconv
 	make
 
 	touch build-stamp