patch 8.1.0857: indent functionality is not separated

Problem:    Ignore functionality is not separated.
Solution:   Move indent functionality into a new file. (Yegappan Lakshmanan,
            closes #3886)
diff --git a/src/Make_morph.mak b/src/Make_morph.mak
index ae49041..6bcae1a 100644
--- a/src/Make_morph.mak
+++ b/src/Make_morph.mak
@@ -48,6 +48,7 @@
 	getchar.c						\
 	hardcopy.c						\
 	hashtab.c						\
+	indent.c						\
 	json.c							\
 	list.c							\
 	main.c							\