Pass declare_signature's argument by value.

`parse_type_section` doesn't need the value after passing it, and this
allows callees to avoid cloning if they need their own copy.

lib/wasm/src/environ/dummy.rs

@@ -350,8 +350,8 @@ impl<'data> ModuleEnvironment<'data> for DummyEnvironment {
         self.info.config
     }
 
-    fn declare_signature(&mut self, sig: &ir::Signature) {
-        self.info.signatures.push(sig.clone());
+    fn declare_signature(&mut self, sig: ir::Signature) {
+        self.info.signatures.push(sig);
     }
 
     fn declare_func_import(

lib/wasm/src/environ/spec.rs

@@ -250,7 +250,7 @@ pub trait ModuleEnvironment<'data> {
     fn reserve_signatures(&mut self, _num: u32) {}
 
     /// Declares a function signature to the environment.
-    fn declare_signature(&mut self, sig: &ir::Signature);
+    fn declare_signature(&mut self, sig: ir::Signature);
 
     /// Provides the number of imports up front. By default this does nothing, but
     /// implementations can use this to preallocate memory if desired.

lib/wasm/src/sections_translator.rs

@@ -48,7 +48,7 @@ pub fn parse_type_section(
                         .expect("only numeric types are supported in function signatures");
                     AbiParam::new(cret_arg)
                 }));
-                environ.declare_signature(&sig);
+                environ.declare_signature(sig);
             }
             ref s => panic!("unsupported type: {:?}", s),
         }