7.8.4 is was released only ten months ago; it surprises me that we'd consider it acceptable to have such a recent release fail to work on new machines when the fix is so small as to not even require a patch to the source tree. In particular, I remember hearing proponents of 7.10's changes reassure detractors that if they choose, they can continue to use 7.8.4, which is no longer an option.
I'd ask that we (1) reconsider the decision to stop 7.8 releases, and (2) if we stand by the decision, document the mitigations for users who would like to build their own working version of the compiler. I just finished a build from a source dist with `unix-2.7.1.0` and it still triggers the El Capitan error, so I suspect it's not as simple as just dropping the new package into `/libraries/unix/`.