[clang] [CIR] Upstream pointer subtraction handling (PR #163306)

[Andy Kaylor via cfe-commits]

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@@ -0,0 +1,35 @@
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -fclangir -emit-cir %s -o %t.cir
+// RUN: FileCheck --check-prefix=CIR --input-file=%t.cir %s
+// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -fclangir -emit-llvm %s -o %t.ll
+// RUN: FileCheck --check-prefix=LLVM --input-file=%t.ll %s
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andykaylor wrote:

```suggestion
// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -fclangir -emit-llvm %s -o %t-cir.ll
// RUN: FileCheck --check-prefix=LLVM --input-file=%t-cir.ll %s
// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -emit-llvm %s -o %t.ll
// RUN: FileCheck --check-prefix=OGCG --input-file=%t.ll %s
```
These added RUN lines will test LLVM IR without using the ClangIR path. That's useful for manually reviewing the differences in the LLVM IR generated. Can you add OGCG checks below corresponding to the things you're checking in the LLVM checks?

https://github.com/llvm/llvm-project/pull/163306