use the mingw dll files (fix #6309)

appveyor.yml

@@ -54,7 +54,7 @@ install:
     - cmd: mklink C:\Python34-x64\python3.exe C:\Python34-x64\python.exe
     - set PATH=%PATH%;C:\Python34-x64
     # expose the dll files
-    - set "PATH=%PATH%;%CYG_ROOT%/usr/x86_64-w64-mingw32/sys-root/mingw/bin"
+    - set "PATH=%CYG_ROOT%/usr/x86_64-w64-mingw32/sys-root/mingw/bin;%PATH%"
     - choco install awscli
 
 build_script: