Set the RULE_LAUNCH_* global properties when CTEST_USE_LAUNCHERS is on.

CTestUseLaunchers is automatically included when you include(CTest). However, it is split out into its own module file so projects can use the CTEST_USE_LAUNCHERS functionality independently.

To use launchers, set CTEST_USE_LAUNCHERS to ON in a ctest -S dashboard script, and then also set it in the cache of the configured project. Both cmake and ctest need to know the value of it for the launchers to work properly. CMake needs to know in order to generate proper build rules, and ctest, in order to produce the proper error and warning analysis.

For convenience, you may set the ENV variable CTEST_USE_LAUNCHERS_DEFAULT in your ctest -S script, too. Then, as long as your CMakeLists uses include(CTest) or include(CTestUseLaunchers), it will use the value of the ENV variable to initialize a CTEST_USE_LAUNCHERS cache variable. This cache variable initialization only occurs if CTEST_USE_LAUNCHERS is not already defined.