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

[Rainer Orth via llvm-commits]

rorth wrote:

Your last change brought the Solaris/sparcv9 failures down to just one:
```
  AddressSanitizer-sparc-sunos :: TestCases/alloca_vla_interact.cpp
  AddressSanitizer-sparc-sunos-dynamic :: TestCases/alloca_vla_interact.cpp
```
same as reported before:
```
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!

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