Autogen: Add (CMAKE_)AUTOGEN_ORIGIN_DEPENDS support

This adds

- the variable ``CMAKE_AUTOGEN_ORIGIN_DEPENDS`` which initializes
- the target property ``AUTOGEN_ORIGIN_DEPENDS``

which controls whether or not the origin target dependencies
should be forwarded to the corresponding ``_autogen`` target.

The default value of ``CMAKE_AUTOGEN_ORIGIN_DEPENDS`` is ``ON``
which corresponds to the behavior that is in place since CMake 3.9.

Closes: #18493

Modules/CMakeGenericSystem.cmake

@@ -23,6 +23,8 @@ set(CMAKE_DL_LIBS "dl")
 
 set(CMAKE_FIND_LIBRARY_PREFIXES "lib")
 set(CMAKE_FIND_LIBRARY_SUFFIXES ".so" ".a")
+
+set(CMAKE_AUTOGEN_ORIGIN_DEPENDS ON)
 set(CMAKE_AUTOMOC_COMPILER_PREDEFINES ON)
 set(CMAKE_AUTOMOC_MACRO_NAMES "Q_OBJECT" "Q_GADGET" "Q_NAMESPACE")