attempt to avoid race condition when initializing list of async signals * cxx-signal-helpers.cc: New file. Move (async_signals): New file-scope static const variable. (octave_block_async_signals, octave_unblock_async_signals, signal_watcher, octave_create_interrupt_watcher_thread): Move functions here from signal-wrappers.c. Use file-scope async_signals variable instead of calling octave_async_signals to get list of asynchronous signals. (init_async_signals): Rename from octave_async_signals and move here from signal-wrappers.cc. Return sigset_t object instead of pointer to static storage that is local to the function. * module.mk: Update.

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