Understand newly introduced "ASCII" encoding

usr.bin/mklocale/mklocale.1

@@ -140,6 +140,8 @@ Followed by a
 which indicates the encoding mechanism to be used for this locale.
 The current encodings are:
 .Bl -tag -width ".Dv MSKanji"
+.It Dv ASCII
+American Standard Code for Information Interchange.
 .It Dv BIG5
 The
 .Dq Big5

usr.bin/mklocale/yacc.y

@@ -118,6 +118,7 @@ table	:	entry
 
 entry	:	ENCODING STRING
 		{ if (strcmp($2, "NONE") &&
+		      strcmp($2, "ASCII") &&
 		      strcmp($2, "UTF-8") &&
 		      strcmp($2, "EUC") &&
 		      strcmp($2, "GBK") &&