Fix up 27173e3735ff.

[Misc #18891]

This commit implements Objects on Variable Width Allocation. This allows
Objects with more ivars to be embedded (i.e. contents directly follow the
object header) which improves performance through better cache locality.

* print `ruby_debug_log_mode` at first.
* show filters when `ruby_debug_log_mode` is not "disabled".

`RUBY_DEBUG_LOG_FILTER` specified only function names but this
patch also check file names for each log events.
If you specify `file:` or `func:` prefix, it's only filter
file names or func names (otherwize check both).

  foo
  # show log when file or func names are mached with foo

  func:foo
  # show log when func name matches foo

  file:foo
  # show log when file name matches foo

  -file:foo,func:bar
  # show log when file name does not contains foo
  #           and func name matches bar

`rb_th_serial(th)` returns th's serial for debug print purpose.

support reject words with `-word` like
RUBY_DEBUG_LOG_FILTER=-foo,-bar,baz,boo`.

`rb_thread_t::serial` is auto-incremented serial number for
threads and it can overflow, it means the serial is not a ID
for each thread, it is only for debug print.

`RUBY_DEBUG_LOG` shows this information.

Also skip EC related information if EC is NULL. This patch
enable to use `RUBY_DEBUG_LOG` without setup EC.

`USE_RUBY_DEBUG_LOG` was only defined when `RUBY_DEVEL` is defined.
This patch removes this dependency (`USE_RUBY_DEBUG_LOG` is defined
independently from `RUBY_DEVEL`).

Do not commit a patch which enables `USE_RUBY_DEBUG_LOG`.