Cross build (Unix => Unix) documentaion

[rodneybrown@pmsc.com]

(egcs-1.1b & egcs-19981012
    - building egcs-1.1.pgcc on linux cross compiling to SCO 3.2v4.1)

Please update gcc/install.texi => gcc/INSTALL to describe where
target platform include files must be install for a cross-build
 - to have fixincludes run.
Should it be $(tooldir)/sys-include now?
Is the $(tooldir)/include directory needed at all?

Please also add a reference to gcc/INSTALL for Unix => Unix cross compiles
in the cross-faq

The following reference from gcc/ChangeLog.0 seems to imply a sys-include
directory - that worked for fixincludes.

Tue May 19 22:31:20 1998  Jeffrey A Law  (law@cygnus.com)

    * Makefile.in (deduced.h): Only run scan-types if $(SYSTEM_HEADER_DIR)
    exists.
    (stmp-fixproto): Simlarly for running fixproto.
    * cross-make (SYSTEM_HEADER_DIR): Now $(tooldir)/sys-include.


Having put in a link from include to sys-include the resultant search
list is as follows.

GNU CPP version pgcc-2.91.57 19980901 (egcs-1.1 release) (80386, ATT syntax)
#include "..." search starts here:
#include <...> search starts here:
 /usr/local/lib/gcc-lib/i486-pc-sco3.2v4.1/pgcc-2.91.57/include
 /usr/local/i486-pc-sco3.2v4.1/sys-include
 /usr/local/i486-pc-sco3.2v4.1/include
End of search list.