ci: add libcpp hardening flags to macOS fuzz job

Follows up to
bitcoin#33425 (comment).

Author: fanquake

ci/test/00_setup_env_mac_native_fuzz.sh

@@ -8,7 +8,7 @@ export LC_ALL=C.UTF-8
 
 export CONTAINER_NAME="ci_mac_native_fuzz"  # macos does not use a container, but the env var is needed for logging
 export CMAKE_GENERATOR="Ninja"
-export BITCOIN_CONFIG="-DBUILD_FOR_FUZZING=ON -DCMAKE_EXE_LINKER_FLAGS='-Wl,-stack_size -Wl,0x80000'"
+export BITCOIN_CONFIG="-DBUILD_FOR_FUZZING=ON -DCMAKE_EXE_LINKER_FLAGS='-Wl,-stack_size -Wl,0x80000' -DAPPEND_CPPFLAGS='-D_LIBCPP_HARDENING_MODE=_LIBCPP_HARDENING_MODE_DEBUG'"
 export CI_OS_NAME="macos"
 export NO_DEPENDS=1
 export OSX_SDK=""