Added mingw to platforms where we build libiconv

Adding libiconv for mingw platform as our build host ubuntu-16 lacks the win-iconv-mingw-w64-dev package.
If we upgrade our build host to ubuntu-20 or newer we can rely on that system package instead.

Ticket: ENT-12744
Changelog: none

Author: craigcomstock

build-scripts/compile-options

@@ -123,8 +123,10 @@ case "$OS_FAMILY" in
 esac
 
 # iconv is needed for libxml2 on some platforms
+# ENT-12744 - adding libiconv for mingw platform as our build host ubuntu-16 lacks the win-iconv-mingw-w64-dev package.
+# If we upgrade our build host to ubuntu-20 or newer we can rely on that system package instead.
 case "$OS_FAMILY" in
-   aix|solaris)  var_append DEPS "libiconv" ;;
+   mingw|aix|solaris)  var_append DEPS "libiconv" ;;
 esac
 
 var_append DEPS "libxml2 libyaml"