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, 3 insertions, 3 deletions

diff --git a/documentation/src/wayland.dox b/documentation/src/wayland.dox
index 9df242e08..4836f9c1f 100644
--- a/documentation/src/wayland.dox
+++ b/documentation/src/wayland.dox
@@ -191,7 +191,7 @@ without any other change in the source code nor to the application's environment
 
 In special situations, such as with embedded systems equipped with the Wayland software but lacking
 the X11 library, it's possible to build the FLTK library such as it contains only the Wayland backend.
-This is achieved building FLTK with <tt>cmake -DOPTION_WAYLAND_ONLY=on</tt> or with
+This is achieved building FLTK with <tt>cmake -DFLTK_BACKEND_X11=OFF</tt> or with
 <tt>configure --disable-x11</tt>. In that case, FL/fl_config.h does not define
 \c FLTK_USE_X11.
 
@@ -1120,7 +1120,7 @@ build system, preprocessor variable \c USE_SYSTEM_LIBDECOR is 1,
 and both \c libdecor and its plugin are loaded at run-time from shared libraries.
 When these packages are not available or are at an earlier version, FLTK uses the bundled
 copy of \c libdecor.
-When CMake \c OPTION_USE_SYSTEM_LIBDECOR is OFF, FLTK uses the bundled \c libdecor copy
+When CMake \c FLTK_USE_SYSTEM_LIBDECOR is OFF, FLTK uses the bundled \c libdecor copy
 even if shared libraries \c libdecor.so and \c libdecor-gtk.so are installed.
 This option is ON by default.
 
@@ -1133,7 +1133,7 @@ However, if environment variable \c LIBDECOR_FORCE_CSD is defined to value \c 1
 FLTK app runs, \c libdecor instructs an SSD-able compositor to refrain from decorating its
 windows and decorates windows itself.
 
-Whatever the value of \c OPTION_USE_SYSTEM_LIBDECOR, FLTK and \c libdecor use environment variable
+Whatever the value of \c FLTK_USE_SYSTEM_LIBDECOR, FLTK and \c libdecor use environment variable
 \c LIBDECOR_PLUGIN_DIR as follows: if this variable is defined and points to the name of a directory,
 this directory is searched for a potential \c libdecor plugin in the form of a shared library;
 if one is found, FLTK and \c libdecor load it and use it.