patch 8.1.2081: the spell.c file is too big

Problem:    The spell.c file is too big.
Solution:   Move the code for spell suggestions to a separate file. (Yegappan
            Lakshmanan, closes #4988)
diff --git a/src/Make_morph.mak b/src/Make_morph.mak
index 0f3cd4e..9c070c8 100644
--- a/src/Make_morph.mak
+++ b/src/Make_morph.mak
@@ -94,6 +94,7 @@
 	sign.c							\
 	spell.c							\
 	spellfile.c						\
+	spellsuggest.c						\
 	syntax.c						\
 	tag.c							\
 	term.c							\