Add a function to parse a btrace xml document into a vector of branch trace
blocks.
gdb/
* features/btrace.dtd: New file.
* Makefile.in (XMLFILES): Add btrace.dtd.
* btrace.h (parse_xml_btrace): New declaration.
* btrace.c: Include xml-support.h.
(parse_xml_btrace): New function.
(parse_xml_btrace_block): New function.
(block_attributes): New struct.
(btrace_attributes): New struct.
(btrace_children): New struct.
(btrace_elements): New struct.
