[Patch, libstdc++/64584, libstdc++/64585] Clear basic_regex after imbue and make assign exception tolerant

[Jonathan Wakely]

>@@ -675,12 +681,22 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> 	assign(const basic_string<_Ch_type, _Ch_typeraits, _Alloc>& __s,
> 	       flag_type __flags = ECMAScript)
> 	{
>+	  auto __traits = _M_traits;
>+	  auto __f = _M_flags;
> 	  _M_flags = __flags;
>-	  _M_original_str.assign(__s.begin(), __s.end());
>-	  auto __p = _M_original_str.c_str();
>-	  _M_automaton = __detail::__compile_nfa(__p,
>-						 __p + _M_original_str.size(),
>-						 _M_traits, _M_flags);
>+	  _M_traits = __traits;

What is this assignnment for?

>+	  __try
>+	    {
>+	      _M_automaton = __detail::__compile_nfa(
>+	        __s.data(), __s.data() + __s.size(), _M_traits, _M_flags);
>+	      _M_original_str = __s;
>+	    }
>+	  __catch (...)
>+	    {
>+	      _M_traits = __traits;
>+	      _M_flags = __f;
>+	      __throw_exception_again;
>+	    }
> 	  return *this;
> 	}
>
>@@ -767,8 +786,10 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
>       swap(basic_regex& __rhs)
>       {
> 	std::swap(_M_flags, __rhs._M_flags);
>-	std::swap(_M_original_str, __rhs._M_original_str);
>-	this->imbue(__rhs.imbue(this->getloc()));
>+	std::swap(_M_traits, __rhs._M_traits);
>+	auto tmp = std::move(_M_original_str);

Please rename this to __tmp to avoid user-defined macros.

>+	this->assign(__rhs._M_original_str, _M_flags);
>+	__rhs.assign(tmp, __rhs._M_flags);
>       }
>
> #ifdef _GLIBCXX_DEBUG