gcc-4.5: Update gxx headers patch

This patch now expects gxx-include-dir
to be specified under sysroot which we
already do through gcc-cross4.inc from
oe-core

Please test

Signed-off-by: Khem Raj <raj.khem@gmail.com>
Signed-off-by: Koen Kooi <koen@dominion.thruhere.net>