Log Message:
libspiro: update to 1.5.0.20240903.

- 2024-Sep-03
    * Libspiro Version 20240902 (1.5.0)
    * Downgraded configure.ac PRE_REQ(2.70) to 2.69 for ELN distros.

- 2024-Sep-02
    * Libspiro Version 20240902 (1.4.0)
    * Bugfix - seen in fontforge issue 5209. Reverted code to remove
      (incorrectly coded) pointer tests which seemed like a good idea
      back then, but are of low value. Removed it to prioritize speed.
    * Removed config.sub and config.guess since these are generated at
      'autoreconf -i;automake' time, which may contain newer versions.
    * configure.ac updated from 2.64 to 2.70 due to obsolete warnings.
    * Libspiro code seems relatively mature and stable at this point.