Versions 4.3 and above only come packaged as .tar.gz and .tar.lz,
and the lzip decompressor is less commonly readily available, thus
switch back to the .tar.gz format.
This command isn't a standard tool; different distributions have
different implementations, and e.g. Fedora doesn't ship it by
default.
Settle on using "command -v $tool >/dev/null" for tests about whether
a tool is available. (We could also use "hash $tool 2>/dev/null" as we
already had in build-all.sh, but settling on using "command -v"
everywhere, for consistency and simplicity.)
Printing '<triple>' causes the shell to try to read a file named
triple. One could either quote it, or just remove the angle brackets;
removing the brackets for simplicity.
Martin Storsjö