[Bug libstdc++/68397] std::tr1::expint fails in __expint_En_cont_frac for some long double arguments due to low __max_iter value

[3dw4rd at verizon dot net]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68397

--- Comment #1 from Ed Smith-Rowland <3dw4rd at verizon dot net> ---
I concur with this solution.
I can make a patch.