Ignore host includes during cross compilation

[Marcin Juszkiewicz]

As some of you know I came to Linaro from OpenEmbedded project. In OE we cross 
compiled by default and to make it more easy we had one nice addon to gcc.

When host includes were used gcc errored out with "CROSS COMPILE BADNESS: 
/usr/include used" style message. Patch is present in metadata:

http://cgit.openembedded.org/cgit.cgi/openembedded/tree/recipes/gcc/gcc-4.4.4/zecke-
no-host-includes.patch

Some time ago replacement was announced on OE mailing list:

http://thread.gmane.org/gmane.comp.handhelds.openembedded/34169

In that thread Khem Raj mentioned -Wno-poison-system-directories which is 
available in CSL toolchains.

I would like to get that functionality in our cross compiler as this nicely 
shows problems in packages. I got hit by that in eglibc when it fails with:

In file included from ../ports/sysdeps/arm/libc-tls.c:20:0:
../csu/libc-tls.c: In function ‘__libc_setup_tls’:
../csu/libc-tls.c:194:1: error: ‘__ARM_NR_set_tls’ undeclared (first use in 
this function)
../csu/libc-tls.c:194:1: note: each undeclared identifier is reported only 
once for each function it appears in

just because unistd.h used from host instead from target includes.

Regards, 
-- 
JID:      hrw at jabber.org
Website:  http://marcin.juszkiewicz.com.pl/
LinkedIn: http://www.linkedin.com/in/marcinjuszkiewicz