[Bug libstdc++/80506] Wrong magic number in std::gamma_distribution

[emsr at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80506

--- Comment #4 from emsr at gcc dot gnu.org ---
Created attachment 44079
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=44079&action=edit
Patch for trunk and branch-8.

Ok, i was looking at backporting this and there are two more places in 
      gamma_distribution<_RealType>::
      __generate_impl(_ForwardIterator __f, _ForwardIterator __t,
                      _UniformRandomNumberGenerator& __urng,
                      const param_type& __param)
where this same bit is pasted!

So I'll patch trunk on down.