treewide: move NIX_CFLAGS_COMPILE to the env attrset
`nix-eval-jobs --flake ".#legacyPackages.x86_64-linux" --workers 3 2>/dev/null --impure | jq 'select(.error?) | select(.error | match ("attribute set can only contain derivation") )'`
and
`nix-eval-jobs --flake ".#legacyPackages.aarch64-darwin" --workers 3 2>/dev/null --impure | jq 'select(.error?) | select(.error | match ("attribute set can only contain derivation") )'`
no longer has output so this could be all of the remaining issues
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
Upstream has officially abandoned the project as of 2021 [0], there's been
no release since 2016, it uses the EoL Qt 4, and alternatives like
KeePassXC exist.
Also move KeePassXC to its own directory -- it doesn't make sense to
have it in KeePassX's folder anymore.
[0]: https://www.keepassx.org/index.html%3Fp=636.html
