[Dev-C++] what is -fnative-struct?

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Hi,
I would compile GTK+ with Dev-C++.
For example, in project directory of Dev-Cpp, I would compile editor or 
work files.
But I had errors with -fnative-struct.
Is it a descript file required?
What is for?

Please inform me.

I am using Dev-C++ ver. 5 beta. on WinXP.