Help: Document CMAKE_RULE_MESSAGES variable

Fixes: #18368

Help/manual/cmake-variables.7.rst

@@ -78,6 +78,7 @@ Variables that Provide Information
    /variable/CMAKE_PROJECT_VERSION_TWEAK
    /variable/CMAKE_RANLIB
    /variable/CMAKE_ROOT
+   /variable/CMAKE_RULE_MESSAGES
    /variable/CMAKE_SCRIPT_MODE_FILE
    /variable/CMAKE_SHARED_LIBRARY_PREFIX
    /variable/CMAKE_SHARED_LIBRARY_SUFFIX

Help/prop_gbl/RULE_MESSAGES.rst

@@ -8,6 +8,6 @@ progress message describing what each build rule does.  If the
 property is not set the default is ON.  Set the property to OFF to
 disable granular messages and report only as each target completes.
 This is intended to allow scripted builds to avoid the build time cost
-of detailed reports.  If a ``CMAKE_RULE_MESSAGES`` cache entry exists
+of detailed reports.  If a :variable:`CMAKE_RULE_MESSAGES` cache entry exists
 its value initializes the value of this property.  Non-Makefile
 generators currently ignore this property.

Help/variable/CMAKE_RULE_MESSAGES.rst

@@ -0,0 +1,8 @@
+CMAKE_RULE_MESSAGES
+-------------------
+
+Specify whether to report a message for each make rule.
+
+If set in the cache it is used to initialize the value of the :prop_gbl:`RULE_MESSAGES` property.
+Users may disable the option in their local build tree to disable granular messages
+and report only as each target completes in Makefile builds.