Fix leak in libc NFSv4 ACL flags parsing

Free memory allocated by strdup() in parse_flags_verbose().

Submitted by:	Andrew Walker <walker.aj325_gmail.com>
Reported by:	valgrind
Reviewed by:	allanjude, freqlabs, rpokala
Sponsored by:	iXsystems, Inc.
Differential Revision:	https://reviews.freebsd.org/D29871

(cherry picked from commit dd55911)

lib/libc/posix1e/acl_support_nfs4.c

@@ -142,9 +142,10 @@ parse_flags_verbose(const char *strp, uint32_t *var,
     int *try_compact)
 {
 	int i, found, ever_found = 0;
-	char *str, *flag;
+	char *str, *flag, *to_free;
 
 	str = strdup(strp);
+	to_free = str;
 	*try_compact = 0;
 	*var = 0;
 
@@ -166,12 +167,12 @@ parse_flags_verbose(const char *strp, uint32_t *var,
 				    "invalid flag \"%s\"", flags_name, flag);
 			else
 				*try_compact = 1;
-			free(str);
+			free(to_free);
 			return (-1);
 		}
 	}
 
-	free(str);
+	free(to_free);
 	return (0);
 }