[MIPS] Accept SIGTRAP from __builtin_trap
[MIPS] Accept SIGTRAP from __builtin_trap

Implementation of __builtin_trap will raise SIGTRAP on MIPS, so the code
accepts the return error raised by SIGTRAP (fixes untrusted_check test
regression).

NOTRY=true
However, I have run a try job manually, and it passed fine, but CQ has
some issues, and this is a workaround for it.

BUG= run_untrusted_check_test fails on MIPS
TEST= ./scons platform=mips32 run_untrusted_check_test

Review URL: https://codereview.chromium.org/323093004

git-svn-id: 721b910a23eff8a86f00c8fd261a7587cddf18f8@13327 fcba33aa-ac0c-11dd-b9e7-8d5594d729c2

sbc100/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client