CMake: refactor and reformat CMake files

- raise minimum CMake version from 2.6.3 to 3.2.3 (Jun 01, 2015)
- indent all CMake files according to the CMP (2 col.)
- refactor FLTK version number definitions and usage
- unify CMake and autoconf/configure variable names:
  - FL_VERSION -> FLTK_VERSION
  - FL_MAJOR_VERSION -> FLTK_VERSION_MAJOR
  - etc. for _MINOR_ and _PATCH_, respectively
  - note: this does not affect FL_VERSION etc. in source code
- generate "export headers" for all libraries (experimental: OFF)
- port some forgotten goodies from branch-1.3 to master
- merge and improve macro 'create_example' (WIP)
- remove "temporary" options and code for older CMake versions
- include and use 'GenerateExportHeader' (experimental, WIP: OFF)
  - note: created header files are not yet used
- build only *one* DLL with Visual Studio (tested, works)
  - similar to the bundled IDE projects in 1.3.x
- add some dynamically linked test/demo programs ('*-shared')
  if shared libraries are built (WIP)
- split 'macros.cmake': use one file per macro

1 files changed, 47 insertions, 0 deletions

diff --git a/CMake/fl_debug_var.cmake b/CMake/fl_debug_var.cmake
new file mode 100644
index 000000000..4cecf3c7a
--- /dev/null
+++ b/CMake/fl_debug_var.cmake
@@ -0,0 +1,47 @@
+#
+# Macro used by the CMake build system for the Fast Light Tool Kit (FLTK).
+# Written by Michael Surette
+#
+# Copyright 1998-2020 by Bill Spitzak and others.
+#
+# This library is free software. Distribution and use rights are outlined in
+# the file "COPYING" which should have been included with this file.  If this
+# file is missing or damaged, see the license at:
+#
+#     https://www.fltk.org/COPYING.php
+#
+# Please see the following page on how to report bugs and issues:
+#
+#     https://www.fltk.org/bugs.php
+#
+
+#######################################################################
+# fl_debug_var - a macro to output debugging info
+#######################################################################
+#
+# This macro displays the name and value of a CMake variable.
+# The variable name is expanded with spaces to be (at least)
+# <min_len> (currently 24) characters wide for better readability.
+# VARNAME must be a string literal, e.g. WIN32 or "WIN32".
+#
+# Syntax:
+#   fl_debug_var(VARNAME)
+#
+# Example:
+#   fl_debug_var(WIN32)
+#   fl_debug_var("UNIX")
+#
+#######################################################################
+
+macro (fl_debug_var name)
+  set (min_len 24)
+  set (var "${name}")
+  string(LENGTH "${var}" len)
+  while (len LESS min_len)
+    # add one space until min_len is reached
+    # ** string(APPEND var " ") # requires CMake 3.4.x (otherwise loop...)
+    set (var "${var} ")
+    string(LENGTH "${var}" len)
+  endwhile (len LESS min_len)
+  message (STATUS "${var} = '${${name}}'")
+endmacro (fl_debug_var)