patch 8.1.2057: the screen.c file is much too big

Problem:    The screen.c file is much too big.
Solution:   Split it in three parts. (Yegappan Lakshmanan, closes #4943)
diff --git a/src/Make_cyg_ming.mak b/src/Make_cyg_ming.mak
index 9d8abf8..281d147 100644
--- a/src/Make_cyg_ming.mak
+++ b/src/Make_cyg_ming.mak
@@ -719,6 +719,8 @@
 	$(OUTDIR)/dict.o \
 	$(OUTDIR)/diff.o \
 	$(OUTDIR)/digraph.o \
+	$(OUTDIR)/drawline.o \
+	$(OUTDIR)/drawscreen.o \
 	$(OUTDIR)/edit.o \
 	$(OUTDIR)/eval.o \
 	$(OUTDIR)/evalbuffer.o \