renderer: swizzle sampler border color channel if we emulate alpha format

(this got a bit mangled in patchwork, I undid that)
Reviewed-by: Dave Airlie <airlied@redhat.com>

src/vrend_renderer.c

@@ -4241,8 +4241,18 @@ static void vrend_apply_sampler_state(struct vrend_context *ctx,
       }
    }
 
-   if (memcmp(&tex->state.border_color, &state->border_color, 16) || set_all)
+   bool is_emulated_alpha = vrend_format_is_emulated_alpha(res->base.format);
+   if (memcmp(&tex->state.border_color, &state->border_color, 16) || set_all ||
+       is_emulated_alpha) {
+      if (is_emulated_alpha) {
+         union pipe_color_union border_color;
+         border_color = vstate->base.border_color;
+         border_color.ui[0] = border_color.ui[3];
+         border_color.ui[3] = 0;
+         glTexParameterIuiv(target, GL_TEXTURE_BORDER_COLOR, border_color.ui);
+      } else
          glTexParameterIuiv(target, GL_TEXTURE_BORDER_COLOR, state->border_color.ui);
+   }
    tex->state = *state;
 }