we don't remove the entire feature in one go to make review easier.
impure derivations are rather unintrusive on their own, at least if
we compare them to dynamic or ca derivations in general, so we will
be done with this soon. as it stands impure derivations cannot work
without ca derivations, and those we *really* want to leave behind.
Change-Id: I4f01d8d758b2c85dcd6c3078304b5ee1b52f65b0
clangd broke because it can't look through symlinks. compile_commands
manipulation does not fix it, clangd configuration does not fix it, a
vfs overlay does not fix it, and while a combination of those can fix
it with a bind mount in place that's just too cursed to even consider
clangd bug: https://github.com/llvm/llvm-project/issues/116877
Change-Id: I8e3e8489548eb3a7aa65ac9d12a5ec8abf814aec
eldritch horrors