Fix warning for Android NDK compiler: "function declaration without a prototype is deprecated in all versions of C [-Wstrict-prototypes]"

https://stackoverflow.com/questions/42125/warning-error-function-declaration-isnt-a-prototype
In C int foo() and int foo(void) are different functions. int foo() accepts an arbitrary number of arguments, while int foo(void) accepts 0 arguments. In C++ they mean the same thing.

src/render/direct3d12/SDL_render_d3d12.c

@@ -1200,7 +1200,7 @@ done:
     return result;
 }
 
-static DXGI_MODE_ROTATION D3D12_GetCurrentRotation()
+static DXGI_MODE_ROTATION D3D12_GetCurrentRotation(void)
 {
     /* FIXME */
     return DXGI_MODE_ROTATION_IDENTITY;