ci: Add a fractional deqp run of softpipe with asan enabled.

This should help us avoid landing memory leaks (and some buffer overflows)
throughout the GL stack.  I put the asan lib in x86_test-base because
we'll want asan for lavapipe, too.

This requires keeping debug symbols for the asan drivers in the artifacts,
as otherwise you can't do much with the backtraces it produces.

Closes: #3726
Reviewed-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/8530>

.gitlab-ci/prepare-artifacts.sh

@@ -18,7 +18,9 @@ if [ -n "$CROSS" ]; then
 else
     STRIP="strip"
 fi
-find install -name \*.so -exec $STRIP {} \;
+if [ -z "$ARTIFACTS_DEBUG_SYMBOLS"]; then
+    find install -name \*.so -exec $STRIP {} \;
+fi
 
 # Test runs don't pull down the git tree, so put the dEQP helper
 # script and associated bits there.