[llvm] r199886 - Prevent repetitive warnings for unrecognized processors and features

[Artyom Skrobov]

> Our documentation is not very good surrounding some of these larger
> architectural issues. However, I can tell you with certainty that
> this patch is unacceptable in it's current state. Revert it.
>
> As David said, it violates a fundamental invariant of the LLVM
> codebase, which is that library users in the same process can
> independently use the LLVM library. (There are some unfortunate
> historical deviations from this that are being slowly mended,
> but going new code doesn't regress on this: it's not up for debate).

Reverted as r200083, but I'd still appreciate any hints as to what can be an
acceptable solution to the issue at hand (preventing the same warning from
being reported multiple times from multiple calling points).

If the documentation doesn't guide around these larger architectural issues,
and the existing code cannot be trusted as an example to follow, then the
only remaining option I can see is to submit patches at random, until one of
them gets accepted.