Defect: Edit GCC's download_prerequisites script for macOS

[rouson]

EDIT by @zbeekman on 4/12/2017 13:21 EDT s/digital signature/checksum/

Installation/build problem

When building an unreleased branch (e.g., trunk) of GCC, the OpenCoarrays installer invokes GCC's download_prerequisites script. As of GCC 7, the latter script uses sha512sum or md5 to verify the digital a signature checksum for each downloaded file. On macOS, the corresponding verification programs differ in name and/or arguments. A pull request will be submitted shortly to enable the OpenCoarrays edit_GCC_download_prereqs_file_if_necessary.sh script to edit the download_prerequisites script to support macOS.