r-4.0.0 - add gmp

https://gitlab.com/ifb-elixirfr/cluster/r-packages/-/jobs/702214268#L226

* installing *source* package 'gmp' ...
** package 'gmp' successfully unpacked and MD5 sums checked
** using staged installation
configure: error: GNU MP not found, or not 4.1.4 or up, see http://gmplib.org
ERROR: configuration failed for package 'gmp'
* removing '/shared/mfs/data/dev/software/miniconda/envs/r-4.0.0/lib/R/library/gmp'
Error in install.packages(package, lib, repos) : 
  installation of package 'gmp' had non-zero exit status
Calls: withCallingHandlers -> install.packages
Execution halted