[libc++abi][NFC] Add comment on long reaching #if

GitOrigin-RevId: 2f21f5b06a490396af10359b32c6313521e526a1
diff --git a/src/cxa_default_handlers.cpp b/src/cxa_default_handlers.cpp
index 800204c..49e21c9 100644
--- a/src/cxa_default_handlers.cpp
+++ b/src/cxa_default_handlers.cpp
@@ -93,10 +93,10 @@
 
 static constexpr std::terminate_handler default_terminate_handler = demangling_terminate_handler;
 static constexpr std::terminate_handler default_unexpected_handler = demangling_unexpected_handler;
-#else
+#else // !LIBCXXABI_SILENT_TERMINATE
 static constexpr std::terminate_handler default_terminate_handler = ::abort;
 static constexpr std::terminate_handler default_unexpected_handler = std::terminate;
-#endif
+#endif // !LIBCXXABI_SILENT_TERMINATE
 
 //
 // Global variables that hold the pointers to the current handler