[clang] [clang][analyzer] Add checker 'core.NullPointerArithm' (PR #157129)

[Donát Nagy via cfe-commits]

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@@ -72,6 +74,9 @@ class DereferenceChecker
   const DerefBugType FixedAddressBug{&FixedDerefChecker,
                                      "Dereference of a fixed address",
                                      "a dereference of a fixed address"};
+  const BugType NullPointerArithmBug{
+      &NullPointerArithmChecker,
+      "Possible undefined arithmetic operation involving a null pointer"};
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NagyDonat wrote:

```suggestion
      "Possibly undefined arithmetic operation involving a null pointer"};
```
I think this is a bit more correct grammatically.

https://github.com/llvm/llvm-project/pull/157129