Binutils and GDB have recently renamed their tarballs due to a GPL compliance issue, and the old tarballs are now missing. The binutils guys were kind enough to provide legacy symlinks so that scripts using the old versions continue to work; the issue has been reported here and here to gdb as well. This means that crosstool-NG releases so far choke when trying to download gdb. A fix to crosstool-NG to use the new versions is coming soon, but in the meantime, you’ll have to manually download the tarballs, and rename them to the old names.