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/isa/x64/inst/mod.rs

@@ -6,7 +6,7 @@ use crate::isa::x64::abi::X64ABIMachineSpec;
 use crate::isa::x64::inst::regs::pretty_print_reg;
 use crate::isa::x64::settings as x64_settings;
 use crate::isa::CallConv;
-use crate::machinst::*;
+use crate::{machinst::*, trace};
 use crate::{settings, CodegenError, CodegenResult};
 use alloc::boxed::Box;
 use alloc::vec::Vec;
@@ -2236,7 +2236,7 @@ impl MachInst for Inst {
     }
 
     fn gen_move(dst_reg: Writable<Reg>, src_reg: Reg, ty: Type) -> Inst {
-        log::trace!(
+        trace!(
             "Inst::gen_move {:?} -> {:?} (type: {:?})",
             src_reg,
             dst_reg.to_reg(),