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/FL/x11.H b/FL/x11.H
index a79cf38f8..c3473020b 100644
--- a/FL/x11.H
+++ b/FL/x11.H
@@ -38,7 +38,7 @@ extern Window fl_x11_xid(const Fl_Window *win);
 extern Fl_Window *fl_x11_find(Window xid);
 /** Returns the X11-specific currently active graphics context.  */
 extern GC fl_x11_gc();
-/** Returns the Cairo-specific currently active graphics context (OPTION_USE_CAIRO=On) */
+/** Returns the Cairo-specific currently active graphics context (FLTK_GRAPHICS_CAIRO=On) */
 extern cairo_t* fl_cairo_gc();
 #else // ! FL_DOXYGEN