[clang] [CIR] Implement CIRBasicAliasAnalysis::getUnderlyingObject (PR #215683)

[Erich Keane via cfe-commits]

erichkeane wrote:

> Hi @andykaylor , thank you for working on this!
> 
> Unfortunately, looks like the test fails validation. Fixed in #216286

Ah, yeah, those look like they crossed in the air :D  A separate patch made that require (for ABI purposes) so anything that got its CI before then is probably going to be a pain that way :/

https://github.com/llvm/llvm-project/pull/215683