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

cmake/sdlplatform.cmake

@@ -13,10 +13,7 @@ macro(SDL_DetectCMakePlatform)
     elseif(CMAKE_SYSTEM_NAME MATCHES ".*tvOS.*")
       set(SDL_CMAKE_PLATFORM tvOS)
     elseif(CMAKE_SYSTEM_NAME MATCHES ".*iOS.*")
-      # !!! FIXME: remove the version check when we start requiring >= 3.14.0
-      if(CMAKE_VERSION VERSION_LESS 3.14)
-        set(SDL_CMAKE_PLATFORM iOS)
-      endif()
+      set(SDL_CMAKE_PLATFORM iOS)
     endif()
   elseif(CMAKE_SYSTEM_NAME MATCHES "Haiku.*")
     set(SDL_CMAKE_PLATFORM Haiku)
@@ -57,7 +54,7 @@ macro(SDL_DetectCMakePlatform)
   elseif(CMAKE_SYSTEM_NAME MATCHES "QNX.*")
     set(SDL_CMAKE_PLATFORM QNX)
   elseif(CMAKE_SYSTEM_NAME MATCHES "BeOS.*")
-    message_error("BeOS support has been removed as of SDL 2.0.2.")
+    message(FATAL_ERROR "BeOS support has been removed as of SDL 2.0.2.")
   endif()
 
   if(SDL_CMAKE_PLATFORM)