Bug 491855 - Enabling CoreText should be explicit instead of magically enabled based on the SDK version, r=ted

configure.in

@@ -3196,9 +3196,23 @@ case "$target" in
                   ac_cv_have_core_text="yes",
                   ac_cv_have_core_text="no")
   AC_MSG_RESULT([$ac_cv_have_core_text])
-  if test "$ac_cv_have_core_text" = "yes"; then
-    AC_DEFINE(MOZ_CORETEXT, 1)
+
+  case "${target_cpu}" in
+  x86_64)
     MOZ_CORETEXT=1
+    ;;
+  esac
+
+  MOZ_ARG_ENABLE_BOOL(coretext,
+[  --enable-coretext      Use CoreText instead of ATSUI for text rendering],
+    MOZ_CORETEXT=1,
+    MOZ_CORETEXT=)
+
+  if test -n "$MOZ_CORETEXT"; then
+    if test "$ac_cv_have_core_text" = "no"; then
+      AC_MSG_ERROR([--enable-coretext requires MacOS SDK 10.5 or newer])
+     fi
+     AC_DEFINE(MOZ_CORETEXT)
   fi
   ;;
 esac