Move compiltion of asm.js code to parse time.

BUG= https://bugs.chromium.org/p/v8/issues/detail?id=4203
TEST=asm-wasm
R=mtrofin@chromium.org
LOG=N

Review-Url: https://codereview.chromium.org/2141813002
Cr-Commit-Position: refs/heads/master@{#37695}