patch 8.1.1869: code for the argument list is spread out

Problem:    Code for the argument list is spread out.
Solution:   Put argument list code in arglist.c. (Yegappan Lakshmanan,
            closes #4819)
diff --git a/src/Make_morph.mak b/src/Make_morph.mak
index 7616ce2..e478b30 100644
--- a/src/Make_morph.mak
+++ b/src/Make_morph.mak
@@ -25,6 +25,7 @@
 	${CC} ${CFLAGS} $< -o $@
 
 SRC =	arabic.c						\
+	arglist.c						\
 	autocmd.c						\
 	blowfish.c						\
 	buffer.c						\