Implement the Symbol builtin object (#2601)

This patch contains the base functionalities that the new builtin object requires.

Currently unavailable:
 - print (Symbol('foo')) - this features requires the refactor of the print handler function
 - Several global symbol based builtin routines (follow up patch)

JerryScript-DCO-1.0-Signed-off-by: Robert Fancsik frobert@inf.u-szeged.hu

jerry-core/ecma/base/ecma-gc.c

@@ -592,6 +592,9 @@ ecma_gc_free_object (ecma_object_t *object_p) /**< object to free */
 
       switch (ext_object_p->u.class_prop.class_id)
       {
+#ifndef CONFIG_DISABLE_ES2015_SYMBOL_BUILTIN
+        case LIT_MAGIC_STRING_SYMBOL_UL:
+#endif /* !CONFIG_DISABLE_ES2015_SYMBOL_BUILTIN */
         case LIT_MAGIC_STRING_STRING_UL:
         case LIT_MAGIC_STRING_NUMBER_UL:
         {