PHP's run-tests file supports passing a result file using the -W option, although this has to be injected using the TESTS variable:

make test TESTS="-W results.log"

This results in the following output (I've only run a single test):

PASSED  /Users/alcaeus/Code/mongodb/mongo-php-driver/tests/smoketest.phpt

While this file only contains the name of the test and the status, it would allow us to assemble an XUnit file containing information about all tests (including the diff for the corresponding test) which can then be stored on the patch build using Evergreen's attach.results command.