C++ front-end: enum attributes and multiple attributes

Clang's standard library includes enum member attributes and uses of
`__attribute__((...)) __attribute__((...))` rather than combining
multiple attributes via a comma between them.

Author: tautschnig

src/cpp/parse.cpp

@@ -2458,7 +2458,7 @@ bool Parser::rGCCAttribute(typet &t)
 
 bool Parser::optAttribute(typet &t)
 {
-  if(lex.LookAhead(0) == TOK_GCC_ATTRIBUTE)
+  while(lex.LookAhead(0) == TOK_GCC_ATTRIBUTE)
   {
     lex.get_token();
 
@@ -4627,6 +4627,10 @@ bool Parser::rEnumBody(irept &body)
     set_location(n, tk);
     n.set(ID_name, tk.data.get(ID_C_base_name));
 
+    typet discarded_attribute;
+    if(!optAttribute(discarded_attribute))
+      return false;
+
     if(lex.LookAhead(0, tk2)=='=') // set the constant
     {
       lex.get_token(tk2); // read the '='