[clang] [Clang] Fix name lookup for dependent bases (PR #114978)

[Erich Keane via cfe-commits]

erichkeane wrote:

Hmm, that compile time regression is unfortunate.  @vbe-sc as a part of your next version of this patch, can you do some sort of analysis why this would result in further lookups/instantiation/etc?  I could comprehend that perhaps we're skipping the 'current instantiation' now for these bases so now there is more work to do in instantiations (of which there are more of those than the base, sort of out of necessity), but would like some sort of analysis/confirmation that is the case/what is happening in some of those 'worst' comparisons.

https://github.com/llvm/llvm-project/pull/114978