Add simple test for vec_swizzle

test/gtx/gtx_vec_swizzle.cpp

@@ -6,6 +6,27 @@ int main()
 	int Error = 0;
 
 
+
+
+
+	{
+		glm::ivec2 const v(1, 2);
+		Error += xx(v).x != xx(v).y;
+		Error += yy(v).x != yy(v).y;
+	}
+
+	{
+		glm::ivec3 const v(1, 2, 3);
+		Error += zyx(v) != glm::ivec3(3, 2, 1);
+	}
+
+	{
+		glm::ivec4 const v(1, 2, 3, 4);
+		Error += wwww(v) != glm::ivec4(4);
+		Error += wzyx(v) != glm::ivec4(4,3,2,1);
+
+	}
+
 	return Error;
 }