If `CTEST_USE_LAUNCHERS` is `TRUE` in a CTest script then the
`ctest_configure` command will add `-DCTEST_USE_LAUNCHERS:BOOL=TRUE` to
the cmake command used to configure the project. This allows a project
to only set `CTEST_USE_LAUNCHERS` in a ctest script and have launchers
work.
Add variable CTEST_CHANGE_ID to configure the setting. This allows
CTest clients to give CDash information about what change is being
tested so that CDash can take actions to report the results (e.g. to a
pull request page).
