patch 8.0.0742: terminal feature does not work on MS-Windows

Problem:    Terminal feature does not work on MS-Windows.
Solution:   Use libvterm and libwinpty on MS-Windows. (Yasuhiro Matsumoto)
diff --git a/src/Make_cyg_ming.mak b/src/Make_cyg_ming.mak
index 95619c4..0f6a492 100644
--- a/src/Make_cyg_ming.mak
+++ b/src/Make_cyg_ming.mak
@@ -750,6 +750,7 @@
 
 ifeq ($(TERMINAL),yes)
 OBJ += $(OUTDIR)/terminal.o
+VTERM_LIB = libvterm/.libs/libvterm.a
 endif
 
 
@@ -849,7 +850,7 @@
 	$(CC) $(CFLAGS) -o uninstal.exe uninstal.c $(LIB)
 
 $(TARGET): $(OUTDIR) $(OBJ)
-	$(CC) $(CFLAGS) $(LFLAGS) -o $@ $(OBJ) $(LIB) -lole32 -luuid $(LUA_LIB) $(MZSCHEME_LIBDIR) $(MZSCHEME_LIB) $(PYTHONLIB) $(PYTHON3LIB) $(RUBYLIB)
+	$(CC) $(CFLAGS) $(LFLAGS) -o $@ $(OBJ) $(LIB) -lole32 -luuid $(LUA_LIB) $(MZSCHEME_LIBDIR) $(MZSCHEME_LIB) $(PYTHONLIB) $(PYTHON3LIB) $(RUBYLIB) $(VTERM_LIB)
 
 upx: exes
 	upx gvim.exe
@@ -865,6 +866,9 @@
 GvimExt/gvimext.dll: GvimExt/gvimext.cpp GvimExt/gvimext.rc GvimExt/gvimext.h
 	$(MAKE) -C GvimExt -f Make_ming.mak CROSS=$(CROSS) CROSS_COMPILE=$(CROSS_COMPILE) CXX='$(CXX)' STATIC_STDCPLUS=$(STATIC_STDCPLUS)
 
+libvterm/.libs/libvterm.a :
+	cd libvterm && $(MAKE) libvterm.la
+
 clean:
 	-$(DEL) $(OUTDIR)$(DIRSLASH)*.o
 	-$(DEL) $(OUTDIR)$(DIRSLASH)*.res