howto remove /usr/include from standard include dir?

[f.l.]

hi,
i'm building linuxfromscratch,
then comes this question, what's the best way to remove /usr/include
from search path,
but still keep other system dirs as is,
for the target is to be run separately from the host,
headers in /usr/include is not wanted.

so i want to know, if it is good to change gcc/config/i386/linux.h,
add these two lines

  #undef STANDARD_INCLUDE_DIR
  #define STANDARD_INCLUDE_DIR 0

is that ok?

thanks very much.