Always ignore SIGPIPE for NaCl both in SFI mode and non SFI mode.
Currently, if there is an access to the pipe, whose other side is
already closed, SIGPIPE will be raised in some platform such as linux.
It is unexpected behavior, and causes some test failure.
This is what trusted plugin does in content/app/content_main_runner.cc.
TEST=Ran PPAPINaClPNaClNonSfiTest.Audio locally many times and the flakiness
was gone. Also run trybots.