Implement RANDOM using GnuCOBOL's compat

[GitMensch]

There is a non-gmp version which can be enabled with preprocessor options - enable that on GnuCOBOL's configure (uses system rand()). Using the same seeds you should get the same results.

[infinityabundance]

Thanks, I will implement thie non-gmp version as a preprocessor option as well to mirror the upstream.