[llvm] [BoundsChecking] Add guard= pass parameter (PR #122575)

[Vitaly Buka via llvm-commits]

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@@ -29,6 +29,7 @@ class BoundsCheckingPass : public PassInfoMixin<BoundsCheckingPass> {
     };
     std::optional<Runtime> Rt; // Trap if empty.
     bool Merge = false;
+    std::optional<int8_t> GuardKind; // `allow_ubsan_check` argument.
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vitalybuka wrote:

In llvm everything is signed, instructions on values can be signed/unsigned.
We can add more bits, but can do that when needed.

I copied type from ubsantrap() parameter, but at that time I didn't notice that ubsantrap
accepts "CheckHandler" which are not SanitizerKind.

Also uint64_t is unnecessary for SanitizerOrdinal, can be 0-127:
```
  /// Number of array elements. 
  static constexpr unsigned kNumElem = 2;
  /// Mask value initialized to 0.
  uint64_t maskLoToHigh[kNumElem]{};
```

we should add static_assert there to modify ubsantrap if we need more bits.
Better with clang patch for code you mentioned.

https://github.com/llvm/llvm-project/pull/122575