Remove useless -xc++ flag.

Author: RoPP

setup.py

@@ -82,7 +82,7 @@ def spawn(self, cmd):
     flags = ['-I' + os.path.abspath('win32')]
     link_flags = []
 else:
-    flags = ['-fPIC', '-xc++', '-std=c++11', '-Wall', '-Wno-parentheses']
+    flags = ['-fPIC', '-std=c++11', '-Wall', '-Wno-parentheses']
     platform.mac_ver()
     if platform.system() == 'Darwin':
         flags.extend([