A lot of things hard-require the ECM bits that use it now.
Due to some cursed interaction between Qt's use of cmake and our
strictDeps patch, this makes a bunch of builds fall over until
things are moved (or, in some cases, copied) to nativeBuildInputs.
Disabling strictDeps makes things build, but starts leaking build-deps
into the final outputs via the ecm-hook wrapper, so just ADD ALL THE THINGS
for now, and hopefully we can figure out how to do this properly later.
Previously the shebang in khc_mansearch.py pointed to /bin/env and caused it to fail; add python3 to the extraBuildInputs to that it gets converted to a nix path.
Also get the man-db binaries by their nix path rather than hoping that they're in the runtime PATH.
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.
