Refactor gen_x86 to use an interface more like gen_arm and to remove the need for the caller to decide whether an 8-bit or 32-bit displacement is needed in the rdisp functions. Update m68k_to_x86 to use the new version of the gen_x86 functions and do some minor refactoring there in the process

#version 110

attribute vec2 pos;
varying vec2 texcoord;
uniform float width;

void main()
{
	gl_Position = vec4(pos, 0.0, 1.0);
	texcoord = sign(pos) * vec2(width/1024.0, 240.0/-512.0) + vec2(width/1024.0, 240.0/512.0);
}