The nixpkgs-unstable channel's programs.sqlite was used to identify
packages producing exactly one binary, and these automatically added
to their package definitions wherever possible.
with structuredAttrs lists will be bash arrays which cannot be exported
which will be a issue with some patches and some wrappers like cc-wrapper
this makes it clearer that NIX_CFLAGS_COMPILE must be a string as lists
in env cause a eval failure
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
