ci: install llvm-symbolizer

.gitlab-ci.yml

@@ -97,6 +97,8 @@ variables:
     - if [ "$STEM" = yes ]; then apt-get install timelimit; fi
     - if [ "$CC" = clang ]; then apt-get install clang; fi
     - if [ "$NSS" = yes ]; then apt-get install libnss3 libnss3-dev; fi
+    # llvm-symbolizer for sanitizer backtrace
+    - if [ "$HARDENING" = yes ]; then apt-get install llvm; fi
     # TODO: This next line should not be debian-only.
     - if [ "$STEM" = yes ]; then git clone --depth 1 https://git.torproject.org/stem.git ; export STEM_PATH="$(pwd)/stem"; fi
     # TODO: This next line should not be debian-only.