cranelift: Introduce a feature to enable trace logs (#4484)

* Don't use `log::trace` directly but a feature-enabled `trace` macro
* Don't emit disassembly based on the log level

cranelift/codegen/Cargo.toml

@@ -54,6 +54,9 @@ core = ["hashbrown"]
 # can significantly increase the size of the library.
 testing_hooks = []
 
+# Enables detailed logging which can be somewhat expensive.
+trace-log = []
+
 # This enables unwind info generation functionality.
 unwind = ["gimli"]