[libc++] Formalize what configurations are covered by the ABI lists

[libc++] Formalize what configurations are covered by the ABI lists

By encoding ABI-affecting properties in the name of the ABI list, it
makes it clear when an ABI list test should or should not be available,
and what results we should expect.

Note that we clearly don't encode all ABI-affecting parameters in the
name right now -- I just ported over what we supported in the code that
was there previously. As we encounter configurations that we wish to
support but produce different ABI lists, we can add those to the ABI
identifier and start supporting them.

This commit also starts checking the ABI list in the CI jobs that run
a supported configuration. Eventually, all configurations should have
a generated ABI list and the test should even run implicitly as part of
the Lit test suite.

Differential Revision: https://reviews.llvm.org/D92194