Autogen: Reintroduce AUTOUIC lookup path from 3.8.2
Restore AUTOUIC lookup paths from 3.8.2
When encountering an #include "<PATH>ui_<BASE>.h" statement,
search for <BASE>.ui in
<SOURCE_DIR>/<BASE>.ui<SOURCE_DIR>/<PATH><BASE>.ui<AUTOUIC_SEARCH_PATH>/<BASE>.ui<AUTOUIC_SEARCH_PATH>/<PATH><BASE>.ui
In CMake 3.8.2 the lookup list was
<SOURCE_DIR>/<BASE>.ui
In CMake 3.9.[01] the lookup list was
<SOURCE_DIR>/<PATH><BASE.ui><AUTOUIC_SEARCH_PATH>/<PATH><BASE>.ui