[clang] [llvm] [llvm][clang] Allocate a new stack instead of spawning a new thread to get more stack space (PR #133173)

[Reid Kleckner via llvm-commits]

https://github.com/rnk commented:

The premerge tests failed on a modules crash recovery test case on other platforms, and those seem like true positives that need to be fixed.

Overall, I think the main risk with this approach is that it will break in-process, FP-based stack unwinders that validate that the target FP is within the thread's stack limits. Those seem like reasonable assumptions to me, since there's no good way to efficiently determine if an FP value is a legitimate stack address other than to compare against the bounds of the thread stack. That's what gives me caution and makes me want to let this be an Apple-only thing.

https://github.com/llvm/llvm-project/pull/133173