The `_dll` variable contains the target name. The code
was trying to use `_NAME` when handling ABSL_PROPAGATE_CXX_STD.
Probably a cut&paste error from the other places where we
handle that option.

PiperOrigin-RevId: 510551097
Change-Id: I006435978333dd7a72a300503389a7bf48fb6d0d