autotools, cmake, macOS: Do not use the system iconv() by default

backport from PR #9676 by @flibitijibibo

CMakeLists.txt

@@ -242,7 +242,7 @@ endif()
 if(UNIX OR MINGW OR MSYS OR (USE_CLANG AND NOT WINDOWS) OR VITA OR PSP OR PS2 OR N3DS)
   set(OPT_DEF_LIBC ON)
 endif()
-if(WINDOWS OR IOS OR TVOS)
+if(WINDOWS OR DARWIN OR MACOSX OR IOS OR TVOS)
   set(SDL_SYSTEM_ICONV_DEFAULT OFF)
 else()
   set(SDL_SYSTEM_ICONV_DEFAULT ON)

configure

@@ -18816,7 +18816,7 @@ fi
 
 enable_system_iconv_default=yes
 case "$host" in
-  *-*-cygwin*|*-*-mingw*)
+  *-*-cygwin*|*-*-mingw*|*-*-darwin*|*-ios-*)
     enable_system_iconv_default=no
     ;;
 esac

configure.ac

@@ -322,7 +322,7 @@ AC_ARG_ENABLE(libc,
 dnl See whether we are allowed to use system iconv
 enable_system_iconv_default=yes
 case "$host" in
-  *-*-cygwin*|*-*-mingw*)
+  *-*-cygwin*|*-*-mingw*|*-*-darwin*|*-ios-*)
     enable_system_iconv_default=no
     ;;
 esac