Subzero, MIPS32: lowerUnreachable

Patch implements lowerUnreachable and encoding for teq
instruction. To avoid duplicated code, class describing
trap instruction is borrowed from
https://codereview.chromium.org/2339323004/

Review URL: https://codereview.chromium.org/2350903002 .

Patch from Srdjan Obucina <Srdjan.Obucina@imgtec.com>.
7 files changed