rustc 和 clang 在 noundef 方面存在差异,导致隐藏的 sret 指针参数出现 MSAN 失败

Running the below code in msan (`-Zsanitizer=memory`) fails MSAN. A simple Cargo-based repro case can be found at https://GitHub.com/th0br0/bug-rustc-cc-interop-msan.