Added missing source.

sdl.mod/source.bmx

@@ -384,6 +384,7 @@ Import "SDL/src/render/SDL_d3dmath.c"
 Import "SDL/src/render/direct3d/SDL_render_d3d.c"
 Import "SDL/src/render/direct3d/SDL_shaders_d3d.c"
 Import "SDL/src/render/direct3d11/SDL_render_d3d11.c"
+Import "SDL/src/render/direct3d11/SDL_shaders_d3d11.c"
 Import "SDL/src/render/opengl/SDL_render_gl.c"
 Import "SDL/src/render/opengl/SDL_shaders_gl.c"
 Import "SDL/src/sensor/windows/SDL_windowssensor.c"