Hello,

I've attached simple patch with moving of the `thickness` var
(from the x_draw_underwave() src/xterm.c) a little bit below, to get rid of:

xterm.c:3520:61: error: unused variable 'thickness' [-Werror,-Wunused-variable]
  int wave_height = 3 * scale_y, wave_length = 2 * scale_x, thickness = scale_y;

as this variable is used only in a case of !USE_CAIRO

Thank you.