RFC] Clarify the absence of API stability for the *device runtime*

I want to clarify that there is no guarantee the device runtime (aka.
libomptarget-nvptx-sm_XX.bc) has a stable API.

Frankly, we’re still at the stage where we’re making all of this work
for non-trivial production applications; we’re not yet at the stage
where we should be trying to provide cross-version stability on what is
really a compiler-internal interface. We’ve not had a discussion, AFAIK,
where we decided on a stability policy for this interface, it’s an
IR-level interface, and so our default should be to consider it
version-locked to LLVM.


Totally in agreement here. Interface stability is useful but expensive. We’re not at that stage in project maturity yet.