patch 8.1.0825: code for autocommands is mixed with file I/O code

Problem:    Code for autocommands is mixed with file I/O code.
Solution:   Move autocommand code to a separate file. (Yegappan Lakshmanan,
            closes #3863)
diff --git a/src/Make_morph.mak b/src/Make_morph.mak
index 70ab537..ae49041 100644
--- a/src/Make_morph.mak
+++ b/src/Make_morph.mak
@@ -25,6 +25,7 @@
 	${CC} ${CFLAGS} $< -o $@
 
 SRC =	arabic.c						\
+	autocmd.c						\
 	blowfish.c						\
 	buffer.c						\
 	charset.c						\