[libc++abi] Don't leak in test (#119505)
Trying to re-enable a test on bots
https://github.com/llvm/llvm-zorg/blob/bb695735dba75e1a5dced13e836f4f46de464bac/zorg/buildbot/builders/sanitizers/buildbot_functions.sh#L443
When we reach `terminate()` `exc` pointer is not
on the stack, so lsan correctly reports a leak.
