Returns the complex arc hyperbolic cosine of its argument.
    This function is OpenVMS Alpha and Integrity servers only.
    Format
      #include  <complex.h>
      double complex cacosh  (double complex z);
      float complex cacoshf  (float complex z);
      long double complex cacoshl  (long double complex z);
1 – Argument
 z
    A complex value.
2 – Description
    The cacosh functions compute the complex arc hyperbolic cosine of
    z, with a branch cut at values less than 1 along the real axis.
3 – Return Values
    n                  The complex arc hyperbolic cosine value, in
                       the range of a half-strip of non-negative
                       values along the real axis and in the interval
                       [-iπ, +iπ] along the imaginary axis.