* treewide: http -> https sources
This updates the source urls of all top-level packages from http to
https where possible.
* buildtorrent: fix url and tab -> spaces
It's now the default. /cc #19456
This makes a real build simplification, because in our current
bootstrapping+aliases, `gcc6` attribute is not the default compiler
but a derivation *built by* the default compiler.
nix-exec didn't build before this commit already
LV2 is a portable plugin standard for audio systems, similar in scope to LADSPA, VST, AU, and others. The Calf audio plugin pack uses LV2 and Ardour3 has also been updated to support LV2 Plugins