[GCC-XML] Mark templated functions

[Andrej Mitrovic]

> Look in GCC/gcc/cp/xml.c at the xml_add_template_decl function.
> There is a loop to dump member template instantiations.  You could
> start there to look for a way to do this.
> -Brad

That function seems to call xml_add_node to add a tree, but I've no
idea how to even create one. Everything seems to be hidden behind a
sea of macros. :/

If anyone else was able to figure this out, let me know please. Thanks!