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/src/lib.rs

@@ -116,4 +116,15 @@ mod souper_harvest;
 
 pub use crate::result::{CodegenError, CodegenResult};
 
+/// Even when trace logging is disabled, the trace macro has a significant performance cost so we
+/// disable it by default.
+#[macro_export]
+macro_rules! trace {
+    ($($tt:tt)*) => {
+        if cfg!(feature = "trace-log") {
+            ::log::trace!($($tt)*);
+        }
+    };
+}
+
 include!(concat!(env!("OUT_DIR"), "/version.rs"));