Fixed GitHub Actions CI and Clang compiler support

[tdulcet]

• Fixed GitHub Actions CI
  • Replaced unsupported macOS 13 runner with the new macOS 15 Intel runner.
  • Updated to test with Linux and macOS ARM runners.
  • Updated actions/checkout.
  • Updated actions/upload-artifact.
• Fixed Makefile to allow building with the Clang compiler again.
• Fixed ARM builds by commenting out the unused __float128 datatype.
• Fixed permission error with genbundle.sh script on some systems by explicitly running it with Bash.
  • Also fixed the ShellCheck errors.
• Enabled -O3 optimization.
• Updated link to AutoPrimeNet.

This is the same as preda#345, but I thought it might be better to create the pull request here, so that the CI could automatically build and test the executables/binaries for all supported platforms again, for users to then download, since this is where development is occurring.

There are a lot of compiler warnings when using Clang, but it does successfully compile without error. For details, see the Actions tab, click (and approve) the run for this pull request, select any of the Clang jobs and expand the "Script" step.