[turbofan] Don't embed pointer to builtins object in generic lowering.

[turbofan] Don't embed pointer to builtins object in generic lowering.

Accessing the builtins object this way prevents sharing of code across
native contexts; instead we now load the builtin from the context of the
JS operation instead.

R=mstarzinger@chromium.org

Review URL: https://codereview.chromium.org/879433002

Cr-Commit-Position: refs/heads/master@{#26264}