hush: deal with a TODO: move argv_from_re_execing out of globals

hush: deal with a TODO: move argv_from_re_execing out of globals

function                                             old     new   delta
generate_stream_from_string                          156     165      +9
setup_heredoc                                        312     320      +8
re_execute_shell                                     387     391      +4
pseudo_exec_argv                                     129     133      +4
run_pipe                                            1790    1783      -7
clean_up_after_re_execute                             30       -     -30
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(add/remove: 0/1 grow/shrink: 4/1 up/down: 25/-37)            Total: -12 bytes