Replacing unbuffered 'os.fdopen' by proxy object to have a unbuffered stdout solution for Windows and AppVeyor that works on Python 3

cibuildwheel/util.py

@@ -22,3 +22,20 @@ class BuildSkipper(object):
 
     def __repr__(self):
         return 'BuildSkipper(%r)' % ' '.join(self.patterns)
+
+
+# Taken from https://stackoverflow.com/a/107717
+class Unbuffered(object):
+    def __init__(self, stream):
+        self.stream = stream
+
+    def write(self, data):
+        self.stream.write(data)
+        self.stream.flush()
+
+    def writelines(self, datas):
+        self.stream.writelines(datas)
+        self.stream.flush()
+
+    def __getattr__(self, attr):
+        return getattr(self.stream, attr)