Always import all tracing macros for the entire crate instead of piecemeal by module

compiler/rustc_session/src/lib.rs

@@ -14,6 +14,9 @@
 extern crate rustc_macros;
 pub mod errors;
 
+#[macro_use]
+extern crate tracing;
+
 pub mod cgu_reuse_tracker;
 pub mod utils;
 pub use lint::{declare_lint, declare_lint_pass, declare_tool_lint, impl_lint_pass};