On MIPS arch, all memory accesses (including halfword)
must be aligned to their native size or an alignment exception occurs.
The kernel will fix this up, but with performance penalty.

TEST=test-bytecode-generator/CallRuntime
BUG=

Review URL: https://codereview.chromium.org/1423373004

Cr-Commit-Position: refs/heads/master@{#31845}