AUTOMOC warns about missing relevant classes after syncqt.cpp migration

Some platform-specific header files migrated to the common section of Qt modules. These files have internal guards for their content, so AUTOMOC doesn't find any relevant content in there and prints a warning at compile time as following:

AutoMoc: .../src/corelib/kernel/qwineventnotifier.h:0:1: note: No relevant classes found. No output generated.

The solution could be in keeping these header files in platform/feature specific sections, still adding them to a CMake source tree according to public header filter, but disabling AUTOGEN if platform/feature condition is not met.