[Bug libstdc++/67011] division by zero in std::exponential_distribution

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67011

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
One is for std::exponential_distribution and one is for
std::tr1:exponential_distribution. The former is already fixed and the latter
is moribund and we don't really care about it any more.