[Rd] Hyperbolic tangent different results on Windows and Mac

[Jeroen Ooms]

This looks like a bug in mingw-w64 CRT. The problem can be produced
with C++ without R:

  #include <iostream>
  #include <cmath>
  #include <complex>

  int main(){
    std::cout << std::fixed;
    std::complex<double> z(356, 0);
    std::cout << "tanh" << z << " = " << std::tanh(z)
         << " (tanh(356) = " << std::tanh(356) << ")\n";
  }

On OS-X we get:

  tanh(356.000000,0.000000) = (1.000000,-0.000000) (tanh(356) = 1.000000)

But on Windows we get:

  tanh(356.000000,0.000000) = (nan,0.000000) (tanh(356) = 1.000000)

I was also able to reproduce the problem with gcc 6.3 in msys2 so it
has not been fixed upstream. You should file a bug report for
mingw-w64.

FWIF, we have run into NaN edge-case bugs before with mingw-w64.

 - https://sourceforge.net/p/mingw-w64/mingw-w64/ci/6617ebd5fc6b790c80071d5b1d950e737fc670e1/
 - https://github.com/wch/r-source/commit/e9aaf8fdeddf27c2a9078cd214a41475c8ff6f40

I am cc'ing Ray Donnelly who is an expert on mingw-w64.