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.
CMake/compatibility.cmake: define functions and macros to be used
if a particular CMake functionality requires a higher CMake version
than FLTK's minimum CMake version, see 'cmake_minimum_required(...)'
in the root CMakeLists.txt.
Note: target_link_directories() is available since CMake 3.13
