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/..`.

compiler/rustc_codegen_ssa/src/traits/backend.rs

@@ -97,6 +97,7 @@ pub trait CodegenBackend {
         &self,
         ongoing_codegen: Box<dyn Any>,
         sess: &Session,
+        outputs: &OutputFilenames,
     ) -> Result<(CodegenResults, FxHashMap<WorkProductId, WorkProduct>), ErrorReported>;
 
     /// This is called on the returned `Box<dyn Any>` from `join_codegen`