Preparation for adding srt-logger tool

• glib-backports: Add a fallback for G_PID_FORMAT

  See also https://gitlab.gnome.org/GNOME/libglnx/-/merge_requests/55

• log: Add _srt_util_is_verbose

• utils: Return the executable path from _srt_find_myself()

• log: Factor out _srt_journal_stream_fd()

• utils: Add _srt_ignore_sigpipe()

• utils: Make _srt_fd_set_close_on_exec inline and async-signal-safe

  This expands the set of places where we can use it.

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Preparation for !676 (merged).