[D3D12] Make tiled resource toggleable, disable debug layer by default

src/xenia/ui/d3d12/d3d12_api.h

@@ -10,6 +10,8 @@
 #ifndef XENIA_UI_D3D12_D3D12_API_H_
 #define XENIA_UI_D3D12_D3D12_API_H_
 
+#include <gflags/gflags.h>
+
 // This must be included before D3D and DXGI for things like NOMINMAX.
 #include "xenia/base/platform_win.h"
 
@@ -19,4 +21,6 @@
 
 #define XELOGD3D XELOGI
 
+DECLARE_bool(d3d12_tiled_resources);
+
 #endif  // XENIA_UI_D3D12_D3D12_API_H_