[Bug libfortran/93871] COTAN is slow for complex types

[thenlich at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93871

--- Comment #1 from Thomas Henlich <thenlich at gcc dot gnu.org> ---
Created attachment 47883
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=47883&action=edit
Proposed patch for COTAN speedup

This is basically the same method mpc uses internally to compute mpc_tan (only
reversed)