ABSL_ALLOCATOR_NOTHROW clarification

[lano1106]

https://abseil.io/docs/cpp/guides/base says

Within Abseil code, move constructors will not throw except because of allocation if compiled without -DABSL_ALLOCATOR_NOTHROW

it is not clear exactly what defining ABSL_ALLOCATOR_NOTHROW does and where it is supposed to be defined.

If ABSL_ALLOCATOR_NOTHROW is defined Abseil move constructors will not throw all the time?
Will this make the code smaller and faster?
Do you need to recompile the Abseil libraries with the define or adding it when compiling client code is enough?

Thank you,