Returns the complex cosine of its argument.
    This function is supported on OpenVMS Integrity servers and
    Alpha only.
    Format
      #include  <complex.h>
      double complex ccos  (double complex z);
      float complex ccosf  (float complex z);
      long double complex ccosl  (long double complex z);
1 – Argument
 z
    A complex value.
2 – Description
The ccos functions return the complex cosine of z.
3 – Return Values
x The complex cosine value.