Introduce "Modern CMake" in FLTK

This is a big commit and there are too many changes to list them all.
The main changes are:

- rename all CMake build options to 'FLTK_*'
- export library targets with namespace (prefix) 'fltk::'
- standardize shared library target names with suffix '-shared'
- set public build properties on libraries for consumers
- document library names and aliases in README.CMake.txt
- document changes in "Migrating Code from FLTK 1.3 to 1.4"
- partial backwards compatibility for old user projects

Included but not directly related changes:

- fix Windows (Visual Studio) DLL build
- add CMake function fl_debug_target() to show target properties
- don't build test programs if FLTK is a subproject
- internal: reformat CMake code: remove space before '('

Thanks to Matthias and Manolo for their help, testing, and feeback.

1 files changed, 15 insertions, 11 deletions

diff --git a/CHANGES.txt b/CHANGES.txt
index 7ff1e140c..025e1f8e4 100644
--- a/CHANGES.txt
+++ b/CHANGES.txt
@@ -1,4 +1,4 @@
-Changes in FLTK 1.4.0                            Released: ??? ?? 2022
+Changes in FLTK 1.4.0                            Released: Feb ?? 2024
 
   General Information about this Release
 
@@ -9,13 +9,17 @@ Changes in FLTK 1.4.0                            Released: ??? ?? 2022
     CMake can be used to generate Makefiles, IDE project files, and
     several other build systems by using different "generators" provided
     by CMake (for instance Ninja, CodeBlocks, Eclipse, KDevelop3, Xcode, etc.).
-    See README.CMake.txt for more information.
+    FLTK uses "Modern CMake" since release 1.4.0 which simplifies user
+    project build systems significantly.
+    See README.CMake.txt and documentation chapter "Migrating Code from
+    FLTK 1.3 to 1.4" for more information.
 
   - autoconf/configure is still supported by the FLTK team for backwards
-    compatibility with older systems that lack CMake support.
+    compatibility with older systems that lack CMake support. Support of
+    autoconf/configure will be dropped in FLTK 1.5.0.
 
   - FLTK 1.4 introduces a new platform, Wayland, available for recent Linux
-    distributions and FreeBSD. More information in README.Wayland.txt
+    distributions and FreeBSD. For details see README.Wayland.txt.
 
   New Features and Extensions
 
@@ -137,23 +141,23 @@ Changes in FLTK 1.4.0                            Released: ??? ?? 2022
     which allows to draw most scripts supported by Unicode, including CJK
     and right-to-left scripts. FLTK now outputs PostScript that draws
     those scripts in vectorial form. The corresponding CMake option is
-    OPTION_USE_PANGO. The corresponding configure option is --enable-pango.
+    FLTK_USE_PANGO. The corresponding configure option is --enable-pango.
     This option is OFF by default.
   - Configure option --enable-wayland allows to build the FLTK library for
     the new Wayland platform while remaining compatible with X11. The
-    corresponding CMake option is OPTION_USE_WAYLAND. This option is ON by default.
+    corresponding CMake option is FLTK_BACKEND_WAYLAND. This option is ON by default.
   - Configure options --enable-wayland --disable-x11 used together allow to
     build FLTK for the Wayland backend only (no x11 backend). Under CMake, the
-    equivalent is to set both OPTION_USE_WAYLAND and OPTION_WAYLAND_ONLY.
+    equivalent option is to set FLTK_BACKEND_WAYLAND=ON and FLTK_BACKEND_X11=OFF.
   - The new configure option --disable-gdiplus removes the possibility to draw
     antialiased lines and curves on the Windows platform. The corresponding CMake
-    option is OPTION_USE_GDIPLUS.
+    option is FLTK_GRAPHICS_GDIPLUS.
   - The library can be built without support for reading SVG images or writing
     graphics in SVG format using the --disable-svg configure option
-    or turning off OPTION_USE_SVG in CMake.
+    or turning off FLTK_OPTION_SVG in CMake.
   - The library can be built without support for PostScript, thus reducing
     its size, using the --disable-print configure option or turning off
-    OPTION_PRINT_SUPPORT in CMake. That makes classes Fl_PostScript_File_Device,
+    FLTK_OPTION_PRINT_SUPPORT in CMake. That makes classes Fl_PostScript_File_Device,
     Fl_EPS_File_Surface and Fl_Printer (under X11 platform only) ineffective.
   - FLTK's ABI version can be configured with 'configure' and CMake.
     See documentation in README.abi-version.txt.
@@ -161,7 +165,7 @@ Changes in FLTK 1.4.0                            Released: ??? ?? 2022
   Bundled libraries
 
   - Bundled image libraries have been upgraded to newer versions.
-    For details see README.bundled-libs.txt.
+    For details see documentation/src/bundled-libs.dox or online docs.
 
   1.4.0 ABI FEATURES