Remove all the logic related to "exit pipe" on Unix

[adamsitnik]

• Remove all the code related to "exit pipe" on Unix:
  • from the managed layer, including:
    

    ProcessPlayground/Library/SafeChildProcessHandle.Unix.cs

    Line 23 in f2220ca

    private static readonly byte[] s_exitPipeBuffer = new byte[1];

    
    

    ProcessPlayground/Library/SafeChildProcessHandle.Unix.cs

    Line 25 in f2220ca

    private readonly int _exitPipeFd;

    
    

    ProcessPlayground/Library/SafeChildProcessHandle.Unix.cs

    Line 118 in f2220ca

    out int exitPipeFd,

  • from the native layer, including:
  • the spawn_process method:
    

    ProcessPlayground/Library/native/pal_process.c

    Line 159 in dfcd508

    int* out_exit_pipe_fd,

    
    

    ProcessPlayground/Library/native/pal_process.c

    Lines 192 to 195 in dfcd508

    	// Create pipe for exit monitoring (CLOEXEC to avoid other parallel processes inheriting it)
    	if (create_cloexec_pipe(exit_pipe) != 0) {
    	return -1;
    	}

  • for other native methods like try_wait_for_exit_cancellable, try_wait_for_exit, wait_for_exit_or_kill_on_timeout, remove the int exitPipeFd argument and when neither HAVE_KQUEUE or HAVE_PIDFD are defined, set errno = ENOTSUP; and return.