Updated GCC toolchain download URLs in package/package_xmc_index.template.json from deprecated developer.arm.com endpoints to reliable armkeil.blob.core.windows.net mirrors, as this caused issues in some corporate networks.

What's Changed

• README.md: Update hil badge. by @LinjingZhang in #425
• Fix legacy links by @ederjc in #426

Full Changelog: 4.0.0...4.0.1