Use OutputFilenames to generate output file for -Zllvm-time-trace

The resulting profile will include the crate name and will be stored in
the `--out-dir` directory.

This implementation makes it convenient to use LLVM time trace together
with cargo, in the contrast to the previous implementation which would
overwrite profiles or store them in `.cargo/registry/..`.

src/lib.rs

@@ -205,6 +205,7 @@ impl CodegenBackend for CraneliftCodegenBackend {
         &self,
         ongoing_codegen: Box<dyn Any>,
         _sess: &Session,
+        _outputs: &OutputFilenames,
     ) -> Result<(CodegenResults, FxHashMap<WorkProductId, WorkProduct>), ErrorReported> {
         Ok(*ongoing_codegen
             .downcast::<(CodegenResults, FxHashMap<WorkProductId, WorkProduct>)>()