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

[Rainer Orth via llvm-commits]

rorth wrote:

I'm currently building with this patch on Solaris/sparcv9, initially as is.  Later I'm going to enable ASan on 32-bit SPARC to see how this goes (Issue #57626).

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