cmake: Implement placeholder --help-custom-modules compatibility

The implementation of the "cmake --help-custom-modules" was removed
along with the rest of the old help generation infrastructure when
documentation was converted to reStructuredText.  In order to avoid
breaking existing project builds outright when they use a custom command
that runs a command like "cmake --help-custom-modules foo.1", generate
the requested file with placeholder content explaining that the option
is not supported anymore.

1 files changed, 2 insertions, 1 deletions

diff --git a/Source/cmDocumentationFormatter.h b/Source/cmDocumentationFormatter.h
index c7da52c..118f03d 100644
--- a/Source/cmDocumentationFormatter.h
+++ b/Source/cmDocumentationFormatter.h
@@ -28,7 +28,8 @@ public:
   {
     None, Version, Usage, ListManuals,
     ListCommands, ListModules, ListProperties, ListVariables, ListPolicies,
-    OneManual, OneCommand, OneModule, OneProperty, OneVariable, OnePolicy
+    OneManual, OneCommand, OneModule, OneProperty, OneVariable, OnePolicy,
+    OldCustomModules
   };
 };