To be able to use it correctly inside an xml build file where, if the
path is not absolute, it's treated as relative to the build file path
(which is TMP_DIR in several tests of the subsequent commit)
*.kjsm and other files might be received when FileCollection is
used in Gradle as a dependency.
Example: `testCompile project(":$coroutines_core").sourceSets.test.output`
(a popular-ish solution to introduce dependencies between tests)
Alexander Udalov