parse windows.h before any import reaches betterRenderer

Six module interfaces carry windows.h in their fragment, and a fragment's
include guard does not cross the boundary, so a unit that imported first
and included the SDK afterwards parsed it twice: clang reports it as
conflicting redeclarations of BroadcastSystemMessageEx and mismatched
uuids all through the SDK. Same shape as the basic_filebuf failure, one
level further out - the header arrives through d3d12.h, not directly.

Thirty units get a guarded windows.h ahead of everything; on Linux it is
a no-op. Vendored single-header libraries are left alone, and the block
goes after a BOM rather than before it.

betterRenderer/renderer/source/sky.cpp

@@ -1,3 +1,6 @@
+#ifdef _WIN32
+#include <windows.h>   // before any import: its guard must be set here
+#endif
 #include <array>
 #include <limits>
 #include <memory>