issue837 introduced the flag _GLIBCXX_DEBUG which makes debug builds incompatible with libraries that are compiled without the flag. This means that currently, we have no way to run a debug build with an LP configuration.
We discussed a build configuration that disables _GLIBCXX_DEBUG. In issue837 we also discussed disabling the LP components in the (normal) debug build. Maybe we should combine the two suggestions and change the normal debug mode, so it enables _GLIBCXX_DEBUG if and only if no LP component is enabled? An alternative would be to have two debug builds: one with _GLIBCXX_DEBUG that forces all LP components to be disabled, and one without _GLIBCXX_DEBUG. What do you prefer?
(I'm classifying this as a bug because of the undefined behavior that can currently happen in debug LP builds but feel free to demote it if you disagree.)