Software :: Why GCC Includes Files From Unexpected Dirs

Now I'm porting a WIFI driver to my platform, MIPS little endian, Linux-2.6.18, uClibc environment for STB. And I'm experiencing some strange symptom. As you know, there are some kind of include files that system provides such like GCC-provided(usually in /usr/include), LIBC-includes(/usr/include), Linux-includes(${LINUX}/include/linux), ASM-includes(${LINUX}/include/asm) and so on, and there are many files resides different directories as the same name (e.g. time.h, types.h, limits.h ...) and many of them has
different contents.

I'm confusing because that some include files are read from unexpected directories.
The command line is like following. $ cross-gcc -o Target -I$(GCC_INC) -I$(LIB_INC) -I$(appl_inc) -isystem $(LINUX)/include -isystem $(LINUX)/include/linux Source.c

And some symbol means:

GCC_INC: directory for GCC include files.
LIB_INC: directory for LIBC include files.
LINUX: Linux kernel directory.

[code]....

As shown above, some include files are read from unexpected directory. This causes some severe compile errors. I've verified these by adding '-E' to the command line. How can I order GCC to read files from where I'm expect?