Older versions of Emscripten appear to emit Asm.js containing:
HEAP8[x] with x in int
As opposed to the spec legal construct:
HEAP8[x>>0] with x in int

As older programs and even benchmarks such as Embenchen
include these constructs, support them for compatibility.

BUG= https://code.google.com/p/v8/issues/detail?id=4203
TEST=test-asm-validator,mjsunit/asm-wasm
R=aseemgarg@chromium.org,titzer@chromium.org
LOG=N

Review URL: https://codereview.chromium.org/1692713006

Cr-Commit-Position: refs/heads/master@{#33964}