Update to sagemath 8.5.
    
    Also:
    - Bundle ipython again; Fedora version is too far ahead.  Also have to bundle
      prompt_toolkit since Fedora version is too far ahead of bundled ipython.
    - Drop LANGUAGES variable setting, now ignored by the sagemath build system.
    - Drop unused SAGE_CBLAS variable from /usr/bin/sage.
    - Do not force the C locale when launching sagemath.
    - Allow the user to override SAGE_DEBUG in /usr/bin/sage.
    - Add -ecm, -giac, and -latte patches to fix interactions with external tools.
    - Add -sigfpe patch from upstream.