Copy cfg_attrs instead setting it to itself

CfgAttribute copy constructor did not copy cfg_attrs properly.

gcc/rust/ChangeLog:

	* ast/rust-cond-compilation.h: Copy cfg_attrs

Signed-off-by: Pierre-Emmanuel Patry <pierre-emmanuel.patry@embecosm.com>

Author: P-E-P

gcc/rust/ast/rust-cond-compilation.h

@@ -226,7 +226,7 @@ class CfgAttrAttribute
   CfgAttrAttribute (CfgAttrAttribute const &other)
     : config_to_include (
       other.config_to_include->clone_configuration_predicate ()),
-      cfg_attrs (cfg_attrs)
+      cfg_attrs (other.cfg_attrs)
   {}
 
   // Overloaded assignment operator to clone