Revert undefining some defines #103
                
     Merged
            
            
          
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The reverted code undefines
_POSIX_THREADS(and a couple of other defines), which are queried in PythonQt.h.If it is not set on a POSIX system, we get the error:
Require native threads. See https://bugs.python.org/issue31370As far as I can see, none of these defines comes from python.h, at least not in current versions of Python.