Autogen: Add documentation for CMAKE_AUTOGEN_VERBOSE

Help/manual/cmake-variables.7.rst

@@ -290,6 +290,7 @@ Variables that Control the Build
    /variable/CMAKE_ARCHIVE_OUTPUT_DIRECTORY
    /variable/CMAKE_ARCHIVE_OUTPUT_DIRECTORY_CONFIG
    /variable/CMAKE_AUTOGEN_PARALLEL
+   /variable/CMAKE_AUTOGEN_VERBOSE
    /variable/CMAKE_AUTOMOC
    /variable/CMAKE_AUTOMOC_COMPILER_PREDEFINES
    /variable/CMAKE_AUTOMOC_DEPEND_FILTERS

Help/variable/CMAKE_AUTOGEN_VERBOSE.rst

@@ -0,0 +1,13 @@
+CMAKE_AUTOGEN_VERBOSE
+---------------------
+
+Sets the verbosity of :prop_tgt:`AUTOMOC`, :prop_tgt:`AUTOUIC` and
+:prop_tgt:`AUTORCC`.  A positive integer value or a true boolean value
+lets the ``AUTO*`` generators output additional processing information.
+
+Setting :variable:`CMAKE_AUTOGEN_VERBOSE` has the same effect
+as setting the ``VERBOSE`` environment variable during
+generation (e.g. by calling ``make VERBOSE=1``).
+The extra verbosity is limited to the ``AUTO*`` generators though.
+
+By default :variable:`CMAKE_AUTOGEN_VERBOSE` is unset.