AutoMoc: Only add the WIN32 define if the target system is Windows
When there's no moc_predefs.h generated, we add the WIN32 define as fallback.
Before this change, we added the WIN32 define if the host system was Windows. That's wrong when cross-compiling. Now we're checking whether the target system is Windows.
Fixes: #22933 (closed)
Topic-rename: automoc-cross-windows
Edited by Brad King