Change some callers to use pg_ascii_toupper().

The input is ASCII anyway, so it's better to be clear that it's not
locale-dependent.

Discussion: https://postgr.es/m/450ceb6260cad30d7afdf155d991a9caafee7c0d.camel@j-davis.com

src/backend/access/transam/xlogfuncs.c

@@ -479,7 +479,7 @@ pg_split_walfile_name(PG_FUNCTION_ARGS)
 
 	/* Capitalize WAL file name. */
 	for (p = fname_upper; *p; p++)
-		*p = pg_toupper((unsigned char) *p);
+		*p = pg_ascii_toupper((unsigned char) *p);
 
 	if (!IsXLogFileName(fname_upper))
 		ereport(ERROR,

src/backend/utils/adt/cash.c

@@ -1035,7 +1035,7 @@ cash_words(PG_FUNCTION_ARGS)
 	appendStringInfoString(&buf, m0 == 1 ? " cent" : " cents");
 
 	/* capitalize output */
-	buf.data[0] = pg_toupper((unsigned char) buf.data[0]);
+	buf.data[0] = pg_ascii_toupper((unsigned char) buf.data[0]);
 
 	/* return as text datum */
 	res = cstring_to_text_with_len(buf.data, buf.len);