On an ARM host, the registers definitions from cpu.h clash
with /usr/include/sys/ucontext.h. As there are unused, just remove
them.
Cc: Jia Liu <proljc@gmail.com>
Cc: qemu-stable@nongnu.org
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>