patch 8.1.1391: no popup window support

Problem:    No popup window support.
Solution:   Add initial code for popup windows.  Add the 'wincolor' option.
diff --git a/src/Make_cyg_ming.mak b/src/Make_cyg_ming.mak
index 7844e00..f479812 100644
--- a/src/Make_cyg_ming.mak
+++ b/src/Make_cyg_ming.mak
@@ -740,6 +740,7 @@
 	$(OUTDIR)/os_win32.o \
 	$(OUTDIR)/pathdef.o \
 	$(OUTDIR)/popupmnu.o \
+	$(OUTDIR)/popupwin.o \
 	$(OUTDIR)/quickfix.o \
 	$(OUTDIR)/regexp.o \
 	$(OUTDIR)/screen.o \