[llvm] [WIP][SPARC] Allow overaligned `alloca`s (PR #107223)

[via llvm-commits]

koachan wrote:

> ```
> Assertion failed: q == top, file /vol/llvm/src/llvm-project/local/compiler-rt/test/asan/TestCases/alloca_vla_interact.cpp, line 45
> ```
> 
> Linux/sparc64 is worse, but AFAICS none of the failures there are related to this patch, just Linux/sparc64 specific issues.
> 
> Thanks again!

I admit I still find it hard to understand what is this testing, so may I ask for some explaination?
I'm not very familiar with the constructs used there, and, particularly, the asan functions...

https://github.com/llvm/llvm-project/pull/107223