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_bc5.mak b/src/Make_bc5.mak
index 9760d8f..d0d31d4 100644
--- a/src/Make_bc5.mak
+++ b/src/Make_bc5.mak
@@ -525,6 +525,7 @@
 
 vimobj =  \
 	$(OBJDIR)\arabic.obj \
+	$(OBJDIR)\autocmd.obj \
 	$(OBJDIR)\blowfish.obj \
 	$(OBJDIR)\buffer.obj \
 	$(OBJDIR)\charset.obj \