perf machine thread: Remove exited threads by default

'struct thread' values hold onto references to mmaps, DSOs, etc. When a
thread exits it is necessary to clean all of this memory up by removing
the thread from the machine's threads. Some tools require this doesn't
happen, such as auxtrace events, 'perf report' if offcpu events exist or
if a task list is being generated, so add a 'struct symbol_conf' member
to make the behavior optional. When an exited thread is left in the
machine's threads, mark it as exited.

This change relates to commit 40826c45eb0b8856 ("perf thread: Remove
notion of dead threads") . Dead threads were removed as they had a
reference count of 0 and were difficult to reason about with the
reference count checker. Here a thread is removed from threads when it
exits, unless via symbol_conf the exited thread isn't remove and is
marked as exited. Reference counting behaves as it normally does.

Reviewed-by: Adrian Hunter <[email protected]>
Signed-off-by: Ian Rogers <[email protected]>
Cc: Alexander Shishkin <[email protected]>
Cc: Andi Kleen <[email protected]>
Cc: Athira Jajeev <[email protected]>
Cc: Changbin Du <[email protected]>
Cc: Colin Ian King <[email protected]>
Cc: Dmitrii Dolgov <[email protected]>
Cc: German Gomez <[email protected]>
Cc: Huacai Chen <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: James Clark <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: K Prateek Nayak <[email protected]>
Cc: Kajol Jain <[email protected]>
Cc: Kan Liang <[email protected]>
Cc: Leo Yan <[email protected]>
Cc: Li Dong <[email protected]>
Cc: Liam Howlett <[email protected]>
Cc: Mark Rutland <[email protected]>
Cc: Masami Hiramatsu <[email protected]>
Cc: Miguel Ojeda <[email protected]>
Cc: Ming Wang <[email protected]>
Cc: Namhyung Kim <[email protected]>
Cc: Nick Terrell <[email protected]>
Cc: Paolo Bonzini <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Ravi Bangoria <[email protected]>
Cc: Sandipan Das <[email protected]>
Cc: Sean Christopherson <[email protected]>
Cc: Steinar H. Gunderson <[email protected]>
Cc: Vincent Whitchurch <[email protected]>
Cc: Wenyu Liu <[email protected]>
Cc: Yang Jihong <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>

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