cmake: bump minimum required CMake version to 3.16

main features:

- No more sdl-build-options/sdl-shared-build-options/sdl-global-options
- Dependency information is stored on SDL3-collector for sdl3.pc
- Use helper functions to modify the SDL targets;
    - sdl_sources to add sources
    - sdl_glob_sources to add glob soruces
    - sdl_link_dependency to add a link dependency that might also
      appear in sdl3.pc/SDL3Config.cmake
    - sdl_compile_definitions to add macro's
    - sdl_compile_options for compile options
    - sdl_include_directories for include directories
  They avoid repeated checks for existence of the SDL targets
- A nice feature of the previous is the ability to generate
  a sdl3.pc or SDL3Config.cmake that describes its dependencies
  accurately.

various:

- remove duplicate libc symbol list
- add CheckVulkan
- remove unused HAVE_MPROTECT
- add checks for getpagesize

include/build_config/SDL_build_config_emscripten.h

@@ -152,7 +152,6 @@
 #define HAVE_SYSCONF 1
 #define HAVE_CLOCK_GETTIME 1
 /* #undef HAVE_GETPAGESIZE */
-#define HAVE_MPROTECT 1
 #define HAVE_ICONV 1
 
 /* SDL internal assertion support */