fix regression introduced by changeset: 1431:28e9d479aa65 [Use '-p' command line option when running matiec (iec2c)]

Variable matiec_flags in c_ext.py and PythonFileCTNMixin.py is not
used for flags for matiec (IEC to C compiler) actually, but it's used
to compile C-code generated for extensions using normal C-compiler,
like gcc.

import os
from POULibrary import POULibrary

class NativeLibrary(POULibrary):
    def GetLibraryPath(self):
        return os.path.join(os.path.split(__file__)[0], "NativeLib.xml")