[clang] [Clang] Add thousands-separator to "cannot allocate array; evaluated array bound [...] exceeds the limit" diagnostic (PR #211785)

[Ambrose Leeb via cfe-commits]

================
@@ -1429,19 +1429,33 @@ inline const StreamingDiagnostic &operator<<(const StreamingDiagnostic &DB,
   return DB;
 }
 
+inline constexpr uint64_t DiagnosticIntegerSeparatorThreshold = 100'000;
+
+inline std::string formatDiagnosticInteger(const llvm::APInt &Val,
+                                           bool Signed) {
+  bool Small = false;
+  if (Signed) {
+    if (Val.getSignificantBits() <= 64) {
+      int64_t S = Val.getSExtValue();
+      uint64_t Magnitude = S < 0 ? -static_cast<uint64_t>(S) : uint64_t(S);
+      Small = Magnitude < DiagnosticIntegerSeparatorThreshold;
+    }
+  } else if (Val.getActiveBits() <= 64) {
+    Small = Val.getZExtValue() < DiagnosticIntegerSeparatorThreshold;
+  }
----------------
Sirraide wrote:

```suggestion
  if (Val.isSingleWord()) {
    if (Signed) 
        Small = !Val.isMinSignedValue() && std::abs(Val.getSExtValue()) < DiagnosticIntegerSeparatorThreshold;
    else 
        Small = Val.getZExtValue() < DiagnosticIntegerSeparatorThreshold;
  }
```
This deals with the issue that `-INT_MIN` overflows and is a bit simpler imo; it also avoids hard-coding that the word size of an `APInt` is 64 bits, but granted, we do that in quite a few places elsewhere...

https://github.com/llvm/llvm-project/pull/211785