Turn the StringEqualStub and friends into proper TurboFan builtins,
which means that we don't need to do on-demand compilation for those
stubs, and use those to defer lowering of the StringEqual, etc.
simplified operators to effect/control linearization (i.e. move it to
the concurrent recompilation part).

BUG=v8:5428
R=jarin@chromium.org

Review-Url: https://codereview.chromium.org/2363333003
Cr-Commit-Position: refs/heads/master@{#39762}