Split Objective-C keyword parsing to handle the '@' separately.

Because apparently, while designing the Objective-C language, somebody
thought it was a world-class idea to allow any white-space between the
'@' character and the subsequent keyword. With this fix, we now
correctly parse:
    @  dynamic
and:
    @
      selector
and:
    @"foo"
     "bar"
    @"mooze"
(This last one is 1 single string split over multiple lines.)
Wonderful, isn't it?

What we (and Clang) do not support, but what GCC supports is something
like:
   @"foo"@@  "bar"  @"mooze"  @@
which is equivalent to @"foobarmooze".

src/shared/cplusplus/AST.cpp

@@ -1561,14 +1561,16 @@ unsigned SizeofExpressionAST::lastToken() const
 
 unsigned StringLiteralAST::firstToken() const
 {
-    return literal_token;
+    return at_token;
 }
 
 unsigned StringLiteralAST::lastToken() const
 {
     if (next)
         return next->lastToken();
-    return literal_token + 1;
+    if (literal_token)
+        return literal_token + 1;
+    return at_token + 1;
 }
 
 
@@ -1910,7 +1912,7 @@ unsigned ObjCClassForwardDeclarationAST::firstToken() const
     if (attribute_list)
         return attribute_list->firstToken();
 
-    return class_token;
+    return at_token;
 }
 
 unsigned ObjCClassForwardDeclarationAST::lastToken() const
@@ -1921,7 +1923,10 @@ unsigned ObjCClassForwardDeclarationAST::lastToken() const
     else if (identifier_list)
         return identifier_list->lastToken();
 
-    return class_token + 1;
+    else if (class_token)
+        return class_token + 1;
+    else
+        return at_token + 1;
 }
 
 unsigned ObjCProtocolForwardDeclarationAST::firstToken() const
@@ -1929,7 +1934,7 @@ unsigned ObjCProtocolForwardDeclarationAST::firstToken() const
     if (attribute_list)
         return attribute_list->firstToken();
 
-    return protocol_token;
+    return at_token;
 }
 
 unsigned ObjCProtocolForwardDeclarationAST::lastToken() const
@@ -1940,7 +1945,10 @@ unsigned ObjCProtocolForwardDeclarationAST::lastToken() const
     else if (identifier_list)
         return identifier_list->lastToken();
 
-    return protocol_token + 1;
+    else if (protocol_token)
+        return protocol_token + 1;
+    else
+        return at_token + 1;
 }
 
 unsigned ObjCClassDeclarationAST::firstToken() const
@@ -1948,15 +1956,14 @@ unsigned ObjCClassDeclarationAST::firstToken() const
     if (attribute_list)
         return attribute_list->firstToken();
 
-    if (interface_token)
-        return interface_token;
-    else
-        return implementation_token;
+    return at_token;
 }
 
 unsigned ObjCClassDeclarationAST::lastToken() const
 {
     if (end_token)                   return end_token + 1;
+    if (ending_at_token)
+        return ending_at_token + 1;
     if (member_declaration_list)         return member_declaration_list->lastToken();
     if (inst_vars_decl)              return inst_vars_decl->lastToken();
     if (protocol_refs)
@@ -1974,21 +1981,25 @@ unsigned ObjCClassDeclarationAST::lastToken() const
 
     if (interface_token)
         return interface_token + 1;
-    else
+    else if (implementation_token)
         return implementation_token + 1;
+    else
+        return at_token + 1;
 }
 
 unsigned ObjCProtocolDeclarationAST::firstToken() const
 {
     if (attribute_list)
         return attribute_list->firstToken();
-    return protocol_token;
+    return at_token;
 }
 
 unsigned ObjCProtocolDeclarationAST::lastToken() const
 {
     if (end_token)
         return end_token + 1;
+    else if (ending_at_token)
+        return ending_at_token + 1;
 
     else if (member_declaration_list)
         return member_declaration_list->lastToken();
@@ -2001,8 +2012,10 @@ unsigned ObjCProtocolDeclarationAST::lastToken() const
 
     else if (attribute_list)
         return attribute_list->lastToken();
-
-    return protocol_token + 1;
+    else if (protocol_token)
+        return protocol_token + 1;
+    else
+        return at_token + 1;
 }
 
 unsigned ObjCProtocolRefsAST::firstToken() const
@@ -2063,7 +2076,7 @@ unsigned ObjCMessageArgumentAST::lastToken() const
 
 unsigned ObjCProtocolExpressionAST::firstToken() const
 {
-    return protocol_token;
+    return at_token;
 }
 
 unsigned ObjCProtocolExpressionAST::lastToken() const
@@ -2077,7 +2090,10 @@ unsigned ObjCProtocolExpressionAST::lastToken() const
     if (lparen_token)
         return lparen_token + 1;
 
-    return protocol_token + 1;
+    if (protocol_token)
+        return protocol_token + 1;
+
+    return at_token + 1;
 }
 
 unsigned ObjCTypeNameAST::firstToken() const
@@ -2101,7 +2117,7 @@ unsigned ObjCTypeNameAST::lastToken() const
 
 unsigned ObjCEncodeExpressionAST::firstToken() const
 {
-    return encode_token;
+    return at_token;
 }
 
 unsigned ObjCEncodeExpressionAST::lastToken() const
@@ -2109,7 +2125,10 @@ unsigned ObjCEncodeExpressionAST::lastToken() const
     if (type_name)
         return type_name->lastToken();
 
-    return encode_token + 1;
+    if (encode_token)
+        return encode_token + 1;
+
+    return at_token + 1;
 }
 
 unsigned ObjCSelectorWithoutArgumentsAST::firstToken() const
@@ -2147,7 +2166,7 @@ unsigned ObjCSelectorWithArgumentsAST::lastToken() const
 
 unsigned ObjCSelectorExpressionAST::firstToken() const
 {
-    return selector_token;
+    return at_token;
 }
 
 unsigned ObjCSelectorExpressionAST::lastToken() const
@@ -2158,7 +2177,9 @@ unsigned ObjCSelectorExpressionAST::lastToken() const
         return selector->lastToken();
     if (lparen_token)
         return rparen_token + 1;
-    return selector_token + 1;
+    if (selector_token)
+        return selector_token + 1;
+    return at_token + 1;
 }
 
 unsigned ObjCInstanceVariablesDeclarationAST::firstToken() const
@@ -2179,12 +2200,15 @@ unsigned ObjCInstanceVariablesDeclarationAST::lastToken() const
 
 unsigned ObjCVisibilityDeclarationAST::firstToken() const
 {
-    return visibility_token;
+    return at_token;
 }
 
 unsigned ObjCVisibilityDeclarationAST::lastToken() const
 {
-    return visibility_token + 1;
+    if (visibility_token)
+        return visibility_token + 1;
+    else
+        return at_token + 1;
 }
 
 unsigned ObjCPropertyAttributeAST::firstToken() const
@@ -2207,7 +2231,7 @@ unsigned ObjCPropertyDeclarationAST::firstToken() const
     if (attribute_list)
         return attribute_list->firstToken();
 
-    return property_token;
+    return at_token;
 }
 
 unsigned ObjCPropertyDeclarationAST::lastToken() const
@@ -2220,8 +2244,10 @@ unsigned ObjCPropertyDeclarationAST::lastToken() const
         return property_attribute_list->lastToken();
     else if (lparen_token)
         return lparen_token + 1;
-
-    return property_token + 1;
+    else if (property_token)
+        return property_token + 1;
+    else
+        return at_token + 1;
 }
 
 unsigned ObjCMessageArgumentDeclarationAST::firstToken() const
@@ -2354,7 +2380,7 @@ unsigned ObjCFastEnumerationAST::lastToken() const
 
 unsigned ObjCSynchronizedStatementAST::firstToken() const
 {
-    return synchronized_token;
+    return at_token;
 }
 
 unsigned ObjCSynchronizedStatementAST::lastToken() const
@@ -2363,5 +2389,6 @@ unsigned ObjCSynchronizedStatementAST::lastToken() const
     if (rparen_token) return rparen_token + 1;
     if (synchronized_object) return synchronized_object->lastToken();
     if (lparen_token) return lparen_token + 1;
-    return synchronized_token + 1;
+    if (synchronized_token) return synchronized_token + 1;
+    return at_token + 1;
 }