The new macro takes a void(Label* ok, Label* not_ok), which should
generate statements that branch to one of the labels. If the not_ok
Label is reached, it will abort just like CSA_ASSERT.

Also replaces an instance of #ifdef DEBUG ... #endif with this pattern
in builtins-regexp-gen.cc

Change-Id: Ie7ec87e041c040c03f9c528dccc8e709e50ed9b9
Reviewed-on: https://chromium-review.googlesource.com/906933Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Commit-Queue: Dan Elphick <delphick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51178}