d3dx9/tests: Avoid using FP_NAN for portability.

dlls/d3dx9_36/tests/mesh.c

@@ -4809,7 +4809,7 @@ static void test_create_skin_info(void)
             exp_vertices[0] = 0;
             exp_vertices[1] = 0x87654321;
             exp_weights[0] = 0.5;
-            exp_weights[1] = FP_NAN;
+            exp_weights[1] = 0.0f / 0.0f;
             num_influences = 2;
 
             hr = skininfo->lpVtbl->SetBoneInfluence(skininfo, 1, num_influences, vertices, weights);