[Bug libquadmath/68686] tgammaq(x) is always negative for noninteger x < 0

[kahrl at gmx dot net]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68686

--- Comment #2 from kahrl at gmx dot net ---
Created attachment 36909
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=36909&action=edit
Code that compares tgamma and tgammaq. Link with -lm -lquadmath.

When run, generates the two files tgamma.dat and tgammaq.dat which contain the
return values of tgamma and tgammaq, respectively, for input values between
-5.0 and 5.0.

These output files can be used as datafiles with gnuplot to clearly see the
difference between tgamma (correct) and tgammaq (incorrect).