Support build on MacOS
This patch should be deleted after resolving https://github.com/pycurl/pycurl/issues/727
---
--- a/setup.py
+++ b/setup.py
@@ -341,9 +341,6 @@ ignore this message.''')
         if not self.libraries:
             self.libraries.append("curl")
 
-        # Add extra compile flag for MacOS X
-        if sys.platform.startswith('darwin'):
-            self.extra_link_args.append("-flat_namespace")
 
         # Recognize --avoid-stdio on Unix so that it can be tested
         self.check_avoid_stdio()