[coretext] Add version guards for kCTLanguageAttributeName

src/hb-coretext.cc

@@ -698,8 +698,15 @@ retry:
 	CFAttributedStringSetAttribute (attr_string, CFRangeMake (0, chars_len),
 					kCTVerticalFormsAttributeName, kCFBooleanTrue);
       }
+
       if (buffer->props.language)
       {
+/* What's the iOS equivalent of this check?
+ * The symbols was introduced in iOS 7.0.
+ * At any rate, our fallback is safe and works fine. */
+#if MAC_OS_X_VERSION_MIN_REQUIRED < 1090
+#  define kCTLanguageAttributeName CFSTR ("NSLanguage")
+#endif
         CFStringRef lang = CFStringCreateWithCStringNoCopy (kCFAllocatorDefault,
 							    hb_language_to_string (buffer->props.language),
 							    kCFStringEncodingUTF8,