Use non-instanced triangle lists to draw text overlay

* Mesa GL seems like it doesn't like the instanced draw, for whatever
  reason.

renderdoc/data/glsl/text.vert

@@ -33,13 +33,18 @@ layout (location = 1) out vec2 glyphuv;
 
 void main(void)
 {
-	const vec3 verts[4] = vec3[4](vec3( 0.0,  0.0, 0.5),
+	const vec3 verts[6] = vec3[6](vec3( 0.0,  0.0, 0.5),
+                                  vec3( 1.0,  0.0, 0.5),
+                                  vec3( 0.0,  1.0, 0.5),
+
                                   vec3( 1.0,  0.0, 0.5),
                                   vec3( 0.0,  1.0, 0.5),
                                   vec3( 1.0,  1.0, 0.5));
 
-	vec3 pos = verts[VERTEX_ID];
-	uint strindex = uint(INSTANCE_ID);
+	uint vert = uint(VERTEX_ID)%6u;
+
+	vec3 pos = verts[vert];
+	uint strindex = uint(VERTEX_ID)/6u;
 	
 	vec2 charPos = vec2(strindex + pos.x + general.TextPosition.x, pos.y + general.TextPosition.y);