x11/fltk13: Update to 1.3.9

This release does not contain new "ABI features". The ABI (Application
Binary Interface) is 100% compatible with releases 1.3.5 - 1.3.8.

CHANGES IN FLTK 1.3.9                              RELEASED: Dec 09 2023

FLTK 1.3.9 is a maintenance release with some fixes and enhancements.

Highlights in this release:

  - Support macOS up to macOS 14 "Sonoma".

Details:

  Albrecht Schlosser:
    Backport X11 INCR protocol fixes from 1.4.0 (issue #451)
    X11: Suppress compiler warnings when using gcc or clang
    Fix crash if a program exits before it opens a window (STR 3484).
    Fix compilation error with current Visual Studio 2022
    Windows: #define WIN32 if not defined by user
    Backport warning fixes from 1.4.0 in src/fl_draw.cxx (#693)
    Fix compiler warning as pointed out in PR #693
    Fix another compiler warning (#693)
    Remove unused variable, fix "type issue" (#445, part 2)
    Fix stack buffer overflow found by address sanitizer
    Fix "gtk+ rendering" (GitHub Issue #443)
    Fix doxygen warnings
    Bump version numbers, prepare release 1.3.9
    Fix several compiler warnings
    Update bundled image libraries and zlib to current versions
    Update README, README.CMake.txt, and some support files
    Fix compiler warnings: backported from 1.4 (git 'master')
    CMake/MSVC: remove confusing recommendation to rerun CMake
    Documentation: remove dark color on title page
    Raise CMake minimum required version to 3.15 and more

  ManoloFLTK:
    macOS platform: Issue #325
      "Disabling IM disables Greek and Cyrillic layouts"
    Fix fullscreen window level corner cases on macOS
    Fix issue #373 apparent with macOS platform and SDK ? 10.13
    Issue #452: Fl::get_font_name failure on OS-X.
    Issue #454: crash in Fl::get_font_name().
    Issue #469: Fl_Sys_Menu_Bar menu item shortcuts using Esc or Tab
      don't work on Mac
    Fix "Focus is lost leaving full screen on macOS 13" (#608)
    Add support of macOS Ventura 13.0 and macOS Sonoma 14.0
    macOS: remove configure option --enable-x11 and
      CMake OPTION_APPLE_X11; this functionality remains in FLTK 1.4.
    configure.ac: make sure local-png and local-zlib always run together
    Remove the -mwindows argument from CFLAGS and CXXFLAGS

Matthias Melcher:
    Issue #188: Fix reference counts and search for Fl_Shared_Image
      original

  YX:
    Fix IME problem (issue #270)

(micha)