include directory confusion.

[tc lewis <tcl at bunzy dot net>]

hi.  i'm a little confused about how gcc decides in what directories it
looks for include files.  what i'd like to accomplish is to build a gcc
(i'm using 2.95.3 on linux/x86) that looks in /include and nowhere else
(except for its internal headers [prefix/include]).  i don't really want
it looking in /usr/include or /usr/local/include.  the --with-local-prefix
option to configure should aid me in using /include instead of
/usr/local/include, correct?  does the normal --prefix option override the
typical /usr/include path, or is /usr/include hardcoded in elsewhere?

i'm just not certain if i'm reading these docs correctly or not and such.
and i don't really understand the warnings like:
     *Do not* specify `/usr' as the `--with-local-prefix'!  The
     directory you use for `--with-local-prefix' *must not* contain any
     of the system's standard header files.  If it did contain them,
     certain programs would be miscompiled (including GNU Emacs, on
     certain targets), because this would override and nullify the
     header file corrections made by the `fixincludes' script.

or what "fixincludes" does exactly and so on.

is it impossible to combined system and non-system headers in the same
include directory (in my case, /include)?

any clarification would be much appreciated.

-tcl.