Update SDL2 to version 2.28.1.

libs/SDL2/cmake/macros.cmake

@@ -29,7 +29,7 @@ ENDMACRO()
 
 # Message Output
 macro(MESSAGE_WARN _TEXT)
-  message(STATUS "*** WARNING: ${_TEXT}")
+  message(WARNING "${_TEXT}")
 endmacro()
 
 macro(MESSAGE_ERROR _TEXT)
@@ -64,7 +64,7 @@ macro(MESSAGE_TESTED_OPTION _NAME)
   message(STATUS "  ${_NAME}${_PAD}(Wanted: ${_REQVALUE}): ${HAVE_${_STRIPPEDNAME}}")
 endmacro()
 
-macro(LISTTOSTR _LIST _OUTPUT)
+function(LISTTOSTR _LIST _OUTPUT)
   if(${ARGC} EQUAL 3)
     # prefix for each element
     set(_LPREFIX ${ARGV2})
@@ -73,10 +73,12 @@ macro(LISTTOSTR _LIST _OUTPUT)
   endif()
   # Do not use string(REPLACE ";" " ") here to avoid messing up list
   # entries
+  set(res)
   foreach(_ITEM ${${_LIST}})
-    set(${_OUTPUT} "${${_OUTPUT}} ${_LPREFIX}${_ITEM}")
+    set(res "${res} ${_LPREFIX}${_ITEM}")
   endforeach()
-endmacro()
+  set(${_OUTPUT} "${res}" PARENT_SCOPE)
+endfunction()
 
 macro(LISTTOSTRREV _LIST _OUTPUT)
   if(${ARGC} EQUAL 3)
@@ -92,11 +94,15 @@ macro(LISTTOSTRREV _LIST _OUTPUT)
   endforeach()
 endmacro()
 
-if(${CMAKE_VERSION} VERSION_LESS "3.16.0")
+if(CMAKE_VERSION VERSION_LESS 3.16.0 OR SDL2_SUBPROJECT)
+  # - CMake versions <3.16 do not support the OBJC language
+  # - When SDL is built as a subproject and when the main project does not enable OBJC,
+  #   CMake fails due to missing internal CMake variables (CMAKE_OBJC_COMPILE_OBJECT)
+  #   (reproduced with CMake 3.24.2)
   macro(CHECK_OBJC_SOURCE_COMPILES SOURCE VAR)
     set(PREV_REQUIRED_DEFS "${CMAKE_REQUIRED_DEFINITIONS}")
     set(CMAKE_REQUIRED_DEFINITIONS "-x objective-c ${PREV_REQUIRED_DEFS}")
-    CHECK_C_SOURCE_COMPILES(${SOURCE} ${VAR})
+    CHECK_C_SOURCE_COMPILES("${SOURCE}" ${VAR})
     set(CMAKE_REQUIRED_DEFINITIONS "${PREV_REQUIRED_DEFS}")
   endmacro()
 else()
@@ -106,6 +112,13 @@ else()
   endif()
 endif()
 
+if(APPLE)
+  check_language(OBJC)
+  if(NOT CMAKE_OBJC_COMPILER)
+    message(WARNING "Cannot find working OBJC compiler.")
+  endif()
+endif()
+
 if(CMAKE_VERSION VERSION_LESS 3.13.0)
   macro(target_link_directories _TARGET _SCOPE)
     link_directories(${ARGN})