patch 8.1.1886: command line expansion code is spread out

Problem:    Command line expansion code is spread out.
Solution:   Move the code to cmdexpand.c. (Yegappan Lakshmanan, closes #4831)
diff --git a/src/Make_morph.mak b/src/Make_morph.mak
index e478b30..c41e853 100644
--- a/src/Make_morph.mak
+++ b/src/Make_morph.mak
@@ -31,6 +31,7 @@
 	buffer.c						\
 	change.c						\
 	charset.c						\
+	cmdexpand.c						\
 	cmdhist.c						\
 	crypt.c							\
 	crypt_zip.c						\