more liberal view of attribute equality; allow suppressing attr type-checking

src/Attr.cc

@@ -208,7 +208,10 @@ void Attributes::AddAttr(AttrPtr attr, bool is_redef)
 	attrs.emplace_back(attr);
 
 	// We only check the attribute after we've added it, to facilitate
-	// generating error messages via Attributes::Describe.
+	// generating error messages via Attributes::Describe.  If the
+	// instantiator of the object specified a null type, however, then
+	// that's a signal to skip the checking.
+	if ( type )
 		CheckAttr(attr.get());
 
 	// For ADD_FUNC or DEL_FUNC, add in an implicit REDEF, since

src/Attr.h

@@ -86,10 +86,11 @@ public:
 			return false;
 
 		if ( expr || other.expr )
-			// If any has an expression and they aren't the same object, we
+			// Too hard to check for equivalency, since one
-			// declare them unequal, as we can't really find out if the two
+			// might be expressed/compiled differently than
-			// expressions are equivalent.
+			// the other, so assume they're compatible, as
-			return (expr == other.expr);
+			// long as both are present.
+			return expr && other.expr;
 
 		return true;
 		}