[llvm] [RISCV] Adjust max stack-threshold on 64bit systems (PR #208223)

[Bevin Hansson via llvm-commits]

bevin-hansson wrote:

We are seeing UBSan errors coming from the `stack-offset-large.ll` test in StackColoring.cpp, presumably after this patch.
```
llvm/lib/CodeGen/StackColoring.cpp:1235:15: runtime error: signed integer overflow: 2 + 9223372036854775807 cannot be represented in type 'int64_t' (aka 'long')
```

https://github.com/llvm/llvm-project/pull/208223