fix(wasmtime):Config methods should be idempotent (#4252)

This commit refactored `Config` to use a seperate `CompilerConfig` field instead
of operating on `CompilerBuilder` directly to make all its methods idempotent.

Fixes #4189

crates/cranelift/src/builder.rs

@@ -9,7 +9,6 @@ use cranelift_codegen::settings::{self, Configurable, SetError};
 use std::fmt;
 use wasmtime_environ::{CompilerBuilder, Setting, SettingKind};
 
-#[derive(Clone)]
 struct Builder {
     flags: settings::Builder,
     isa_flags: isa::Builder,
@@ -55,10 +54,6 @@ impl CompilerBuilder for Builder {
         self.isa_flags.triple()
     }
 
-    fn clone(&self) -> Box<dyn CompilerBuilder> {
-        Box::new(Clone::clone(self))
-    }
-
     fn target(&mut self, target: target_lexicon::Triple) -> Result<()> {
         self.isa_flags = isa::lookup(target)?;
         Ok(())