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

[Rainer Orth via llvm-commits]

rorth wrote:

> > Just for reference, I've posted the patches I've used for my ASan testing: PR #107403 for the driver side and PR #107405 for enabling the ASan tests in `compiler-rt`.
> 
> Are these patches for Solaris only or do they apply for Linux too? I'd like to try the asan tests too, but after applying them on my Linux box it seems like `check-asan` is still not available:
> 
> ```
> $ ninja check-asan
> ninja: error: unknown target 'check-asan', did you mean 'check-all'?
> ```

The patches work on Linux/sparc64, too.  You don't need the driver one (`clang` on Linux always assumes ASan is supported).  I'd revised the `compiler-rt` test one last night when I managed to avoid hangs in many ASan tests on Linux.  Besides, I've removed `sparcv9` again: while there is some support for that in `compiler-rt`, neither `clang` nor `gcc` have anything matching, so there were hundreds of `sparcv9` ASan failures.  I'm currently finishing one that avoids failures on tests involving stack overflows (works on Solaris already, needs some tweeks for Linux) and posted two testsuite adjustments for ASan on SPARC in general (PRs #108206 and #108200).  There's also one to disable `InstallAtForkHandler` on Linux/sparc64, but that may well be a hack rather than a fix.

I guess it's best if you give me a day or two to finish this stuff.

Thanks a lot for your work, which finally will allow `clang` ASan support to be on par with `gcc`.

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