llvm-project

a6fa21c5 - [CIR] Upstream basic CodeGen tests from incubator (#183998)

[CIR] Upstream basic CodeGen tests from incubator (#183998) This PR upstreams `expressions.cpp` and `c89-implicit-int.c` from the ClangIR incubator to the mainline. Following the incremental approach discussed in #156747 and the feedback from the closed PR #157333, I have: 1. Copied the files directly from the incubator to preserve history. 2. Updated the `RUN` lines to use the `--check-prefix=CIR` flag. 3. Converted `CHECK:` lines to `CIR:`. 4. Standardized variable captures using the `%[[VAR:.*]]` regex syntax (in `expressions.cpp`). Verified locally with `llvm-lit`. This is a partial fix for #156747. *Note: As suggested in previous reviews, I am focusing only on the `CIR` checks for now to keep the upstreaming incremental. OGCG/LLVM verification can be added in a follow-up PR once the base tests land.*