Ninja Multi-Config: Rename variable to be more consistent

Also make some tweaks to the documentation.

Help/generator/Ninja Multi-Config.rst

@@ -19,8 +19,8 @@ the desired ``build-<Config>.ninja`` file with ``ninja -f``. Running
 ``build-<Config>.ninja`` as the ``-f`` file and ``<target>`` as the build
 target.
 
-If :variable:`CMAKE_NINJA_CROSS_CONFIG_ENABLE` is turned on, executables and
-libraries of any configuration can be built regardless of which
+If :variable:`CMAKE_NINJA_MULTI_CROSS_CONFIG_ENABLE` is turned on, executables
+and libraries of any configuration can be built regardless of which
 ``build-<Config>.ninja`` file is used, simply by specifying
 ``<target>:<OtherConfig>`` as the Ninja target. You can also specify
 ``<target>:all`` to build a target in all configurations. Each
@@ -31,8 +31,8 @@ targets will always use the configuration specified in
 Ninja for the same file to be output with different commands in the same build
 graph.
 
-If :variable:`CMAKE_NINJA_CROSS_CONFIG_ENABLE` is not enabled, you can still
-build any target in ``build-<Config>.ninja`` by specifying
+If :variable:`CMAKE_NINJA_MULTI_CROSS_CONFIG_ENABLE` is not enabled, you can
+still build any target in ``build-<Config>.ninja`` by specifying
 ``<target>:<Config>`` or ``<target>``, but not ``<target>:<OtherConfig>`` or
 ``<target>:all``.
 
@@ -60,8 +60,8 @@ This would build the ``Debug`` configuration of ``generator``, which would be
 used to generate ``generated.c``, which would be used to build the ``Debug``
 configuration of ``generated``.
 
-But if :variable:`CMAKE_NINJA_CROSS_CONFIG_ENABLE` is enabled, and you run the
-following instead:
+But if :variable:`CMAKE_NINJA_MULTI_CROSS_CONFIG_ENABLE` is enabled, and you
+run the following instead:
 
 .. code-block:: shell
 

Help/manual/cmake-variables.7.rst

@@ -215,7 +215,6 @@ Variables that Change Behavior
    /variable/CMAKE_MESSAGE_INDENT
    /variable/CMAKE_MESSAGE_LOG_LEVEL
    /variable/CMAKE_MODULE_PATH
-   /variable/CMAKE_NINJA_MULTI_DEFAULT_BUILD_TYPE
    /variable/CMAKE_POLICY_DEFAULT_CMPNNNN
    /variable/CMAKE_POLICY_WARNING_CMPNNNN
    /variable/CMAKE_PREFIX_PATH
@@ -423,7 +422,8 @@ Variables that Control the Build
    /variable/CMAKE_MODULE_LINKER_FLAGS_INIT
    /variable/CMAKE_MSVCIDE_RUN_PATH
    /variable/CMAKE_MSVC_RUNTIME_LIBRARY
-   /variable/CMAKE_NINJA_CROSS_CONFIG_ENABLE
+   /variable/CMAKE_NINJA_MULTI_CROSS_CONFIG_ENABLE
+   /variable/CMAKE_NINJA_MULTI_DEFAULT_BUILD_TYPE
    /variable/CMAKE_NINJA_OUTPUT_PATH_PREFIX
    /variable/CMAKE_NO_BUILTIN_CHRPATH
    /variable/CMAKE_NO_SYSTEM_FROM_IMPORTED

Help/variable/CMAKE_NINJA_CROSS_CONFIG_ENABLE.rst

@@ -1,6 +0,0 @@
-CMAKE_NINJA_CROSS_CONFIG_ENABLE
--------------------------------
-
-If this variable is enabled, cross-configuration building is enabled in the
-:generator:`Ninja Multi-Config` generator. See the generator's description for
-more details.

Help/variable/CMAKE_NINJA_MULTI_CROSS_CONFIG_ENABLE.rst

@@ -0,0 +1,10 @@
+CMAKE_NINJA_MULTI_CROSS_CONFIG_ENABLE
+-------------------------------------
+
+If this variable is enabled, cross-configuration building is enabled in the
+:generator:`Ninja Multi-Config` generator. See the generator's description for
+more details. This variable is ``OFF`` by default.
+
+This variable is meant to be set from the command line (via
+``-DCMAKE_NINJA_MULTI_CROSS_CONFIG_ENABLE:BOOL=ON``) and should not be set from
+project code.