Problem

In `src/frontend/preprocessor/predefined_macros.rs:154`, `DATE` is hardcoded to `"Jan 1 2025"` instead of the actual compilation date. While hardcoding improves build reproducibility, it breaks code that uses `DATE` for build versioning.

GCC uses the actual date unless `SOURCE_DATE_EPOCH` is set for reproducible builds.

```c
const char *built = DATE;
// GCC: "Feb 6 2026" (actual date)
// CCC: always "Jan 1 2025"
```

Suggested approach

Use the actual date by default, but respect `SOURCE_DATE_EPOCH` environment variable for reproducible builds (matching GCC/Clang behavior).

Files to modify

• `src/frontend/preprocessor/predefined_macros.rs` — Use `chrono` or `std::time` for actual date, with `SOURCE_DATE_EPOCH` override

Acceptance criteria

• `DATE` reflects actual compilation date
• `TIME` reflects actual compilation time (if also hardcoded)
• `SOURCE_DATE_EPOCH` env var overrides to a fixed date for reproducibility
• `cargo test --lib` passes