Remove duplicate underscore removal

In order to retain duplicate underscores from original type identifiers.

Invalid character removal is also tweaked to reduce the number of
underscores introduced in the previous step.

Author: thomasspriggs

src/ansi-c/type2name.cpp

@@ -305,23 +305,18 @@ std::string type_name2type_identifier(const std::string &name)
   };
   const auto replace_invalid_characters_with_underscore =
     [](const std::string &identifier) {
-      static const std::regex non_alpha_numeric{"[^A-Za-z0-9]"};
+      static const std::regex non_alpha_numeric{"[^A-Za-z0-9]+"};
       return std::regex_replace(identifier, non_alpha_numeric, "_");
     };
-  const auto remove_duplicate_underscores = [](const std::string &identifier) {
-    static const std::regex duplicate_underscore{"_+"};
-    return std::regex_replace(identifier, duplicate_underscore, "_");
-  };
   const auto strip_leading_non_letters = [](const std::string &identifier) {
     static const std::regex identifier_regex{"[A-Za-z][A-Za-z0-9_]*"};
     std::smatch match_results;
     bool found = std::regex_search(identifier, match_results, identifier_regex);
     POSTCONDITION(found);
     return match_results.str(0);
   };
-  return strip_leading_non_letters(
-    remove_duplicate_underscores(replace_invalid_characters_with_underscore(
-      replace_special_characters(name))));
+  return strip_leading_non_letters(replace_invalid_characters_with_underscore(
+    replace_special_characters(name)));
 }
 
 std::string type_to_partial_identifier(const typet &type, const namespacet &ns)