This service automatically redirects to a mirror that's geographically
closer, which should make downloading the tarballs faster. The GNU
project recommends this instead of bombarding their top-level downloads
site.
Target GDB is only used for debugging the kernel, which is not relevant
to most people. Starting with 924758c6f8, GDB would always be built
as part of the toolchain if the user didn't have it installed. This is
unnecessary.
This commit adds a separate script for building GDB, which the user
needs to explicitly invoke. A message is added to Meta/debug-kernel.sh
which alerts the user to this fact.
