Disable preserve_none under ASAN due to bugs

[morrisonlevi]

See:

• Fully disable preserve_none under ASan llvm/llvm-project#190001, which merged just last week (April 1, 2026)
• Clang-19 crashed: fatal error: error in backend: Stack realignment in presence of dynamic allocas is not supported withthis calling convention. llvm/llvm-project#95928

[iluuu1994]

This is a bit unfortunate, as it makes it impossible to test the tailcall VM with ASAN. The error disappeared for me with Clang 21 (see llvm/llvm-project#95928 (comment)). Which Clang version are you running?

[morrisonlevi]

I had issues on clang 19 (to intentionally match Rust 1.84-1.88 for cross-langauge LTO and other reasons) on aarch64. I saw your comment when looking at the PRs! "Hey, that's a friendly face!" However, the fact that LLVM disabled it in main just a week ago does not give me confidence to enable this for any version, when ASAN is enabled, which is why I opened this PR. They cited issues on x86_64 as well. Thoughts?

[iluuu1994]

However, the fact that LLVM disabled it in main just a week ago does not give me confidence to enable this for any version

Yeah, that's fair. Though it's also possible this is only an issue with C++ in Clang 20+, but not C. Hence I'd prefer only enabling this if we run into an actual issue, especially considering this is exclusively a development configuration.

But ultimately, Arnaud should decide.

[iluuu1994]

Or maybe disable it only for Clang 19 and lower.