gcc: 4.9.2: Add patch to remove a wrong header

This commit adds a patch to gcc removing a unistd.h header include
in libgcc/config/nios2/linux-atomic.c

The file is built as part of GCC first stage (host-gcc-initial),
and so the header is not accesible. Given the header is not needed
it's fine to simply remove it.

Signed-off-by: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>