patch 8.0.0420: text garbled when the system encoding differs from 'encoding'

Problem:    When running :make the output may be in the system encoding,
            different from 'encoding'.
Solution:   Add the 'makeencoding' option. (Ken Takata)
diff --git a/src/Makefile b/src/Makefile
index 0bdd1d4..6e7fdde 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -2157,6 +2157,7 @@
 	test_listlbr \
 	test_listlbr_utf8 \
 	test_lua \
+	test_makeencoding \
 	test_man \
 	test_mapping \
 	test_marks \