THRIFT-4405: fix cygwin on appveyor
diff --git a/build/appveyor/CYGW-appveyor-install.bat b/build/appveyor/CYGW-appveyor-install.bat
index 79b6ef0..72712b2 100644
--- a/build/appveyor/CYGW-appveyor-install.bat
+++ b/build/appveyor/CYGW-appveyor-install.bat
@@ -26,6 +26,12 @@
 CALL cl_showenv.bat                        || EXIT /B
 
 ::
+:: Upgrades cygwin to the latest, if you want...
+::
+:: appveyor DownloadFile "https://cygwin.com/setup-x86_64.exe"
+:: setup-x86_64.exe --quiet-mode --wait --upgrade-also --packages="gcc-g++"
+
+::
 :: Install apt-cyg for package management
 ::