Add and use ASAN blacklist

Blacklist an apparently false positive in the underlying runtime.

.github/workflows/main.yml

@@ -104,6 +104,7 @@ jobs:
         mkdir build && cd build
         # Rust's ASAN requires the build system to explicitly pass a --target triple. We read that
         # value from CMake variable Rust_CARGO_TARGET (shared with corrosion).
+        env CXXFLAGS="$CXXFLAGS -fsanitize-blacklist=$PWD/../build_tools/asan_blacklist.txt" \
             cmake .. -DASAN=1 -DRust_CARGO_TARGET=x86_64-unknown-linux-gnu -DCMAKE_BUILD_TYPE=Debug
     - name: make
       run: |

build_tools/asan_blacklist.txt

@@ -0,0 +1,3 @@
+# Ignore a one-off leak in __cxa_thread_atexit_impl that isn't under our control.
+# See https://github.com/fish-shell/fish-shell/pull/9754#issuecomment-1523782989
+fun:__cxa_thread_atexit_impl