[PATCH] ensure internal print operations are declared before use

Stock rapidxml-1.13 does not allow implementers of the
`rapidxml_print.hpp` header to build under GCC 4.7 (or newer) due to
compliation issues. This is a result of "Name lookup changes" introduced
in GCC 4.7 [1]. The following adds forward declarations required to
compile with GCC 4.7+.

This issue has been mentioned upstream [2], but it has yet to be fixed
in official sources.

[1]: https://gcc.gnu.org/gcc-4.7/porting_to.html
[2]: https://sourceforge.net/p/rapidxml/bugs/16/

Signed-off-by: James Knight <james.knight@rockwellcollins.com>

Index: b/rapidxml_print.hpp
===================================================================
--- a/rapidxml_print.hpp
+++ b/rapidxml_print.hpp
@@ -101,7 +101,16 @@
 
         ///////////////////////////////////////////////////////////////////////////
         // Internal printing operations
-    
+
+        template<class OutIt, class Ch> inline OutIt print_cdata_node(OutIt out, const xml_node<Ch> *node, int flags, int indent);
+        template<class OutIt, class Ch> inline OutIt print_children(OutIt out, const xml_node<Ch> *node, int flags, int indent);
+        template<class OutIt, class Ch> inline OutIt print_comment_node(OutIt out, const xml_node<Ch> *node, int flags, int indent);
+        template<class OutIt, class Ch> inline OutIt print_data_node(OutIt out, const xml_node<Ch> *node, int flags, int indent);
+        template<class OutIt, class Ch> inline OutIt print_declaration_node(OutIt out, const xml_node<Ch> *node, int flags, int indent);
+        template<class OutIt, class Ch> inline OutIt print_doctype_node(OutIt out, const xml_node<Ch> *node, int flags, int indent);
+        template<class OutIt, class Ch> inline OutIt print_element_node(OutIt out, const xml_node<Ch> *node, int flags, int indent);
+        template<class OutIt, class Ch> inline OutIt print_pi_node(OutIt out, const xml_node<Ch> *node, int flags, int indent);
+
         // Print node
         template<class OutIt, class Ch>
         inline OutIt print_node(OutIt out, const xml_node<Ch> *node, int flags, int indent)