ast: builder: Fix arguments of Builder::let

gcc/rust/ChangeLog:

	* ast/rust-ast-builder.h: Mark all arguments as &&.
	* ast/rust-ast-builder.cc (Builder::let): Likewise.

gcc/rust/ast/rust-ast-builder.cc

@@ -215,8 +215,8 @@ Builder::block (std::vector<std::unique_ptr<Stmt>> &&stmts,
 }
 
 std::unique_ptr<Stmt>
-Builder::let (std::unique_ptr<Pattern> pattern, std::unique_ptr<Type> type,
-	      std::unique_ptr<Expr> init) const
+Builder::let (std::unique_ptr<Pattern> &&pattern, std::unique_ptr<Type> &&type,
+	      std::unique_ptr<Expr> &&init) const
 {
   return std::unique_ptr<Stmt> (new LetStmt (std::move (pattern),
 					     std::move (init), std::move (type),

gcc/rust/ast/rust-ast-builder.h

@@ -87,9 +87,9 @@ class Builder
 
   /* Create a let binding with an optional type and initializer (`let <name> :
    * <type> = <init>`) */
-  std::unique_ptr<Stmt> let (std::unique_ptr<Pattern> pattern,
-			     std::unique_ptr<Type> type = nullptr,
-			     std::unique_ptr<Expr> init = nullptr) const;
+  std::unique_ptr<Stmt> let (std::unique_ptr<Pattern> &&pattern,
+			     std::unique_ptr<Type> &&type = nullptr,
+			     std::unique_ptr<Expr> &&init = nullptr) const;
 
   /**
    * Create a call expression to a function, struct or enum variant, given its