* Update SDL dependent code and makefile segments to prepare for SDL3
Many APIs have changed between SDL2 and SDL3. This update adds
preprocessor conditionals to adapt the Maiko SDL code to allow selection of
the SDL major version (2 or 3) from the -DSDL=n define.
The SDL3 implementation is currently available as a preview release, 3.1.0, at
https://github.com/libsdl-org/SDL/releases/tag/prerelease-3.1.0
* Add updates for makefile-haiku.x86_64-sdl to prepare for SDL3
* Allow makeright to accept sdl3 as display type to ease SDL3 experiments
* Update CMakeLists.txt for SDL3 library
* Replaces configuration option -DMAIKO_DISPLAY_SDL=ON/OFF with
-DMAIKO_DISPLAY_SDL=OFF/2/3
* Replaces PUBLIC definitions with PRIVATE definitions on targets since
we are not exporting definitions outside this local compilation
* Update messages to indicate which version of SDL is being configured
* Add fixup for SDL3.xcframework on macOS to compensate for missing
RPATH specification (CMake issue 25998)
Rationalize the SDL.h include file references so that they work on all systems
Use the correct macOS Framework options to get include path and library search path
Add makefile fragments for SDL on macOS on Apple Silicon, plus FreeBSD and Linux
on same cpus as X11
Switch to gcc rather than clang as the default compiler for Linux systems
