breakpad: disable ppc from being built.

../trunk/src/client/linux/dump_writer_common/raw_context_cpu.h:48:2: error: #error "This code has not been ported to your platform yet."
 |  #error "This code has not been ported to your platform yet."

Signed-off-by: Armin Kuster <akuster808@gmail.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>