ci/swrast: Archive Xvfb logs

If anything goes wrong, it's useful to have actual output, as opposed to
guessing from the void.

Signed-off-by: Daniel Stone <daniels@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/31281>

src/gallium/drivers/llvmpipe/ci/gitlab-ci.yml

@@ -38,7 +38,7 @@ llvmpipe:
     weston -Bheadless-backend.so -Swayland-0 --idle-time=0 &
     export WAYLAND_DISPLAY=wayland-0
     section_end weston
-    xvfb-run --server-args='-noreset' bash -c ". $SCRIPTS_DIR/setup-test-env.sh && ${XVFB_SCRIPT}"
+    xvfb-run -e results/xvfb.log --server-args='-noreset' bash -c ". $SCRIPTS_DIR/setup-test-env.sh && ${XVFB_SCRIPT}"
 
 llvmpipe-full:
   extends:

src/gallium/drivers/softpipe/ci/gitlab-ci.yml

@@ -11,7 +11,7 @@ softpipe:
     . "$SCRIPTS_DIR"/setup-test-env.sh
     export LD_LIBRARY_PATH=$CI_PROJECT_DIR/install/lib
     export LIBGL_DRIVERS_PATH=$CI_PROJECT_DIR/install/lib/dri
-    xvfb-run --server-args='-noreset' bash -c ". $SCRIPTS_DIR/setup-test-env.sh && ${XVFB_SCRIPT}"
+    xvfb-run -e results/xvfb.log --server-args='-noreset' bash -c ". $SCRIPTS_DIR/setup-test-env.sh && ${XVFB_SCRIPT}"
 
 softpipe-asan-gles31:
   variables: