patch 8.2.1262: src/ex_cmds.c file is too big

Problem:    src/ex_cmds.c file is too big.
Solution:   Move help related code to src/help.c. (Yegappan Lakshmanan,
            closes #6506)
diff --git a/src/Make_morph.mak b/src/Make_morph.mak
index bd95115..6fc50ed 100644
--- a/src/Make_morph.mak
+++ b/src/Make_morph.mak
@@ -64,6 +64,7 @@
 	gui_xim.c						\
 	hardcopy.c						\
 	hashtab.c						\
+	help.c							\
 	highlight.c						\
 	indent.c						\
 	insexpand.c						\