Priority in including header

Hello.

I am working on embedded linux and I am a beginner.
I am having hard time to port a program on mips board.
As far as I have experienced so far, and two headers of same name exist both below /usr/include and below toolchain directory, header under /usr/include is included.
Am I right?
How can I make compiler include header under toolchain directory.
And when I run configure and look into Makefile, -I/usr/include shows 2 times, I don't know why.

Please help me solve this problem.
Thanks.

You can give a full path name, or you could adjust your path settings so that it finds the include file you want first.