GDK: Fix SDL_pixels.c/_c.h linking error caused by C / C++ mismatch

src/render/direct3d12/SDL_render_d3d12.c

@@ -31,7 +31,6 @@
 #include "../../video/windows/SDL_windowswindow.h"
 #include "../SDL_sysrender.h"
 #include "../SDL_d3dmath.h"
-#include "../../video/SDL_pixels_c.h"
 
 #if defined(SDL_PLATFORM_XBOXONE) || defined(SDL_PLATFORM_XBOXSERIES)
 #include "SDL_render_d3d12_xbox.h"
@@ -78,6 +77,9 @@
 extern "C" {
 #endif
 
+/* This must be included here as the function definitions in SDL_pixels.c/_c.h are C, not C++ */
+#include "../../video/SDL_pixels_c.h"
+
 /* !!! FIXME: vertex buffer bandwidth could be lower; only use UV coords when
    !!! FIXME:  textures are needed. */