re PR libstdc++/67361 (std::regex_error::what() should say something about the error_...

re PR libstdc++/67361 (std::regex_error::what() should say something about the error_code)

	PR libstdc++/67361
	* include/bits/regex_error.h: Add __throw_regex_error that
	supports string.
	* include/bits/regex_automaton.h: Add more specific exception
	messages.
	* include/bits/regex_automaton.tcc: Likewise.
	* include/bits/regex_compiler.h: Likewise.
	* include/bits/regex_compiler.tcc: Likewise.
	* include/bits/regex_scanner.h: Likewise.
	* include/bits/regex_scanner.tcc: Likewise.

From-SVN: r227936