This ordering will simplify streaming processing of xmlo files in
TAMER. Specifically, we know that symbols will have been declared by the
time dependencies are added to the graph (and so we should only be creating
edges to existing nodes); and we can halt reading as soon as the closing
fragments tag is encountered, avoiding parsing the entirety of these massive
XML files.
On one particularly large program, this cuts time down from ~0.333s to
~0.300 in the POC linker.
Mike Gerwitz