Trying to get rid of this Python script looks tempting, because it's currently
the only Python script in the whole `run-make` suite that we actually run.
But getting rid of it would require pulling in a Rust crate to parse XML
instead, and that's probably not worth the extra hassle for a relatively-minor
test.
By placing the stdout in a CDATA block we avoid almost all escaping, as
there's only two byte sequences you can't sneak into a CDATA and you can
handle that with some only slightly regrettable CDATA-splitting. I've
done this in at least two other implementations of the junit xml format
over the years and it's always worked out. The only quirk new to this
(for me) is smuggling newlines as 
 to avoid literal newlines in the
output.
