In 7f530cc5 we taught CTest to pass extra information to CDash at submit
time.  This extra info is used by CDash to initialize a buildid.

`ctest_submit(FILES)` can be used to send specific files to CDash.
These files are not necessarily associated with the build currently
being performed. For this reason, we modify the behavior of ctest_submit()
to only specify this extra info when we are submitting files from the
current build's Testing directory.