ci: more sanitization (for recent changes)

The misaligned accesses were just throwing warnings for me (with gcc),
so I added the flag to stregthen what we get in CI.

.gitlab-ci.yml

@@ -93,7 +93,8 @@ build:
 build-asan:
   <<: *build
   script:
-    - CC=clang CXX=clang++ meson build_ci_asan --default-library=static --prefix=$PREFIX -Db_sanitize=address -Dextra_tests=enabled
+      # "undefined" sanitizer causes C++ issues when loading ahocorasick.so in CI
+    - CC=clang CXX=clang++ CFLAGS=-fno-sanitize-recover=all CXXFLAGS=-fno-sanitize=undefined meson build_ci_asan --default-library=static --prefix=$PREFIX -Db_sanitize=address,undefined -Dextra_tests=enabled
     - ninja -C build_ci_asan
     - ninja -C build_ci_asan install >/dev/null
       # TODO _leaks: not sure what exactly is wrong in leak detection on config tests