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, 1 insertions, 1 deletions

diff --git a/examples/cairo-draw-x.cxx b/examples/cairo-draw-x.cxx
index a11e2db0c..a265dc360 100644
--- a/examples/cairo-draw-x.cxx
+++ b/examples/cairo-draw-x.cxx
@@ -59,7 +59,7 @@ int main(int argc, char **argv) {
 int main(int argc, char **argv) {
     fl_message_title("This program needs a Cairo enabled FLTK library");
     fl_message("Please configure FLTK with Cairo enabled (--enable-cairo or --enable-cairoext)\n"
-               "or one of the CMake options OPTION_CAIRO or OPTION_CAIROEXT, respectively.");
+               "or one of the CMake options FLTK_OPTION_CAIRO_WINDOW or FLTK_OPTION_CAIRO_EXT, respectively.");
     return 0;
 }
 #endif // (FLTK_HAVE_CAIRO)