Update Clang XML LoopNode Output

[stachnik]

r2402 introduced a change to schema regarding the children of an XML LoopNode. Specifically the body child is now a StatementNode rather than a sequence of StatementNodes. Conforming XML output should now have a single BlockNode as the body child which contains the statements which previously would have gone directly under LoopNode. See the ForLoopNode in examples/adder/adder_seq.c.xml for an example.

[tmcclory]

Adjusted the XML generation accordingly.