[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 #2 from Ed Smith-Rowland <3dw4rd at verizon dot net> ---
Created attachment 41198
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=41198&action=edit
Testing a patch...

I'm testing the following:

2017-04-13  Edward Smith-Rowland  <3dw4rd@verizon.net>

        PR libstdc++/68397 std::tr1::expint fails ... long double arguments.
        * include/tr1/exp_integral.tcc: Increase iteration limits.
        * testsuite/tr1/5_numerical_facilities/special_functions/15_expint/
        pr68397.cc: New test.
        * testsuite/special_functions/14_expint/pr68397.cc: New test.