ctest: Consolidate documentation of CTEST_USE_LAUNCHERS (#15533)

The documentation of this variable in the CTest module is outdated
and has been superseded by the ctest(1) manual.  In particular, the
latter mentions that it works with the Ninja generator as well as
makefile generators.  Remove the documentation from the CTest module
and replace it with a link to the main variable documentation (which
already references the ctest(1) manual).

Help/manual/ctest.1.rst

@@ -372,6 +372,8 @@ Options
 
 .. include:: OPTIONS_HELP.txt
 
+.. _`Dashboard Client`:
+
 Dashboard Client
 ================
 
@@ -749,8 +751,9 @@ Configuration settings include:
     initialized by the :command:`build_command` command
 
 ``UseLaunchers``
-  For build trees generated by CMake using a Makefile generator
-  or the :generator:`Ninja` generator, specify whether the
+  For build trees generated by CMake using one of the
+  :ref:`Makefile Generators` or the :generator:`Ninja`
+  generator, specify whether the
   ``CTEST_USE_LAUNCHERS`` feature is enabled by the
   :module:`CTestUseLaunchers` module (also included by the
   :module:`CTest` module).  When enabled, the generated build

Modules/CTest.cmake

@@ -40,21 +40,12 @@ While building a project for submission to CDash, CTest scans the
 build output for errors and warnings and reports them with surrounding
 context from the build log.  This generic approach works for all build
 tools, but does not give details about the command invocation that
-produced a given problem.  One may get more detailed reports by adding::
+produced a given problem.  One may get more detailed reports by setting
+the :variable:`CTEST_USE_LAUNCHERS` variable::
 
   set(CTEST_USE_LAUNCHERS 1)
 
-to the ``CTestConfig.cmake`` file.  When this option is enabled, the CTest
-module tells CMake's Makefile generators to invoke every command in
-the generated build system through a CTest launcher program.
-(Currently the ``CTEST_USE_LAUNCHERS`` option is ignored on non-Makefile
-generators.) During a manual build each launcher transparently runs
-the command it wraps.  During a CTest-driven build for submission to
-CDash each launcher reports detailed information when its command
-fails or warns.  (Setting ``CTEST_USE_LAUNCHERS`` in ``CTestConfig.cmake`` is
-convenient, but also adds the launcher overhead even for manual
-builds.  One may instead set it in a CTest dashboard script and add it
-to the CMake cache for the build tree.)
+in the ``CTestConfig.cmake`` file.
 #]=======================================================================]
 
 #=============================================================================