[Bug libstdc++/58576] std::regex_match() reports mismatched braces on a valid regex

[schwab@linux-m68k.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58576

--- Comment #2 from Andreas Schwab <schwab@linux-m68k.org> ---
[:alnum:] only matches the six characters ":almnu".  If you want to match any
letter or digit you have to write [[:alnum:]].