fix: handle SIGBUS when looking for stack overflows (#4971)

Without this change, a stack overflow on Mac OS during tactic execution
can lead to the message:

    terminated by signal SIGBUS (Misaligned address error)

This comes from `lean_alloc_small`. With the change, the process instead
terminates with the more accurate and actionable:

    Stack overflow detected. Aborting.

src/runtime/stack_overflow.cpp

@@ -107,6 +107,7 @@ void initialize_stack_overflow() {
     action.sa_flags = SA_SIGINFO | SA_ONSTACK;
     action.sa_sigaction = segv_handler;
     sigaction(SIGSEGV, &action, nullptr);
+    sigaction(SIGBUS, &action, nullptr);
 #endif
 }