Fix get library

What is the bug

1. CMake warning pops up when one uses FetchContent without setting the download extract time stamp or CMake Policy 0135.
2. libfortran-support has been made public, but we are still fetching it via ssh.

How do you fix it

Specify CMake Policy 0135, same as here in test/fortran, fetch libfortran-support with https.

How urgent is the bugfix

• I need it as soon as possible
• I can wait for a couple of days
• None of my current codes is directly affected

Mandatory steps before review

• Gitlab CI passes (Hint: use make format for linting)
• Bugfix is covered by additional unit tests
• Mark the merge request as ready by removing Draft:

Mandatory steps before merge

• Reviewed by a maintainer
• Incorporate review suggestions
• Remember to edit the commit message and select the proper changelog category (feature/bugfix/other)
• Prior to merging, please remove any boilerplate from the MR description, retaining only the What is the bug and How do you fix it section to maintain

You are not supposed to merge this request by yourself, the maintainers of libiconmath take care of this action!