As required by the spec, ToJS now throws a TypeError fit I64 values
instead of truncating the I64 value to I32. To throw a TypeError I
introduced a new runtime function because the existing
Runtime::kThrowWasmError does not throw a TypeError. Since we have calls
to two runtime functions now, and an additional one is needed for stack
checks, I extracted the call to runtime functions into a helper function.

R=titzer@chromium.org

TEST=mjsunit/wasm/ffi-error.js:I64InSignatureThrows

Review-Url: https://codereview.chromium.org/2254803002
Cr-Commit-Position: refs/heads/master@{#38718}