patch 8.2.0443: clipboard code is spread out

Problem:    Clipboard code is spread out.
Solution:   Move clipboard code to its own file. (Yegappan Lakshmanan,
            closes #5827)
diff --git a/src/Make_morph.mak b/src/Make_morph.mak
index 2c226de..7273182 100644
--- a/src/Make_morph.mak
+++ b/src/Make_morph.mak
@@ -33,6 +33,7 @@
 	change.c						\
 	charset.c						\
 	cindent.c						\
+	clipboard.c						\
 	cmdexpand.c						\
 	cmdhist.c						\
 	crypt.c							\