gp4prog: Include <cstdlib>
gp4prog: Include <cstdlib>

Some functions used here (e.g. atoi) are supposed to live in <cstdlib>.
Fixes build on macOS.
azonenberg/openfpga,azonenberg/openfpga,rqou/openfpga,azonenberg/openfpga,rqou/openfpga,rqou/openfpga,rqou/openfpga,azonenberg/openfpga,azonenberg/openfpga,rqou/openfpga