Fixes crash of mshtml_winetest:htmldoc (introduced by 716613c). Please do not ask me why.
The test started crashing with commit 716613cddc8039eff5f095051dc9a79727a25e73 "[CMAKE] Use new policies for CMP0005 and CMP0018 (#1481)", which moved this definition from the command line to urlmon_main.h. This got later removed by commit 6c3c2e33f63b9e621497807591555304ecdd37ec "[URLMON] Sync with Wine Staging 4.18. CORE-16441"