Update concepts to check for accidental char_traits usage.

Fixes: https://github.com/boostorg/regex/issues/202.

include/boost/regex/concepts.hpp

@@ -76,13 +76,10 @@ inline long hash_value(char_architype val)
 //
 } // namespace boost
 namespace std{
-   template<> struct char_traits<boost::char_architype>
-   {
-      // The intent is that this template is not instantiated,
-      // but this typedef gives us a chance of compilation in
-      // case it is:
-      typedef boost::char_architype char_type;
-   };
+   //
+   // We should never use this, if we do it should be an error:
+   //
+   template<> struct char_traits<boost::char_architype>;
 }
 //
 // Allocator architype:
@@ -412,6 +409,10 @@ struct BaseRegexConcept
       Regex e5(in1, in2, m_flags);
       ignore_unused_variable_warning(e5);
 
+      // equals:
+      e1 == e2;
+      e1 != e2;
+
       // assign etc:
       Regex e;
       e = m_pointer;

include/boost/regex/v5/basic_regex.hpp

@@ -488,7 +488,7 @@ public:
    }
    //
    // swap:
-   void  swap(basic_regex& that)throw()
+   void  swap(basic_regex& that)noexcept
    {
       m_pimpl.swap(that.m_pimpl);
    }
@@ -533,7 +533,21 @@ public:
          return status() - that.status();
       if(flags() != that.flags())
          return flags() - that.flags();
-      return str().compare(that.str());
+      
+      const char_type* i = m_pimpl->begin();
+      const char_type* j = that.m_pimpl->begin();
+      while ((i != m_pimpl->end()) && (j != that.m_pimpl->end()))
+      {
+         if (*i != *j)
+            return *i < *j ? -1 : 1;
+         ++i;
+         ++j;
+      }
+      if (i != m_pimpl->end())
+         return *i > static_cast<char_type>(0) ? 1 : -1;
+      if (j != that.m_pimpl->end())
+         return *j > static_cast<char_type>(0) ? -1 : 1;
+      return 0;
    }
    bool  operator==(const basic_regex& e)const
    { 

include/boost/regex/v5/pattern_except.hpp

@@ -52,7 +52,7 @@ public:
       , m_position(0)
    {
    }
-   ~regex_error() noexcept override {}
+   ~regex_error() noexcept override = default;
    regex_constants::error_type code()const
    { return m_error_code; }
    std::ptrdiff_t position()const