manuel@vader:~/src/scummvm$ arm-rpi-linux-gnueabi-gcc -isysroot --sysroot=/opt/rpi_root pp.c -o ppp -I/usr/include -I/usr/include/arm-linux-gnueabihf
In file included from /usr/include/stdio.h:27:0,
                 from pp.c:2:
/usr/include/features.h:364:25: fatal error: sys/cdefs.h: No such file or directory
compilation terminated.
manuel@vader:~/src/scummvm$ find /opt/rpi_root -name 'cdefs.h'
/opt/rpi_root/usr/include/arm-linux-gnueabihf/sys/cdefs.h