Fix postgresql-musl: also break lib↔out reference cycle

Previous fix (eee10e3) broke the dev↔out cycle by stripping dev refs
from both $out and $lib. Testing on hydra (standard Nix) revealed a
second cycle: lib↔out. lib embeds out paths (share/locale references
in libpq), and out links against lib. Strip out refs from lib since
shared libraries don't need the binary directory at runtime.

Author: angerman

flake.nix

@@ -173,15 +173,20 @@
              outputChecks = {};
              separateDebugInfo = false;
              disallowedReferences = [];
-             # Break the dev↔out reference cycle: dev references out (via
-             # .pc -L flags), and out references dev (via baked-in paths
-             # in binaries/libs). Strip dev refs from both out and lib
-             # outputs since neither needs dev at runtime.
+             # Break multi-output reference cycles. Nix refuses to register
+             # outputs that form cycles. The cycles are:
+             #   dev ↔ out: dev has .pc files referencing out; out has
+             #              baked-in dev paths from configure
+             #   lib ↔ out: lib has embedded out paths (share/locale refs
+             #              in libpq); out links against lib
+             # Fix: strip dev refs from out+lib, strip out refs from lib.
+             # out→lib is the only legitimate runtime dependency.
              postFixup = (old.postFixup or "") + ''
                find "$out" -name '*.la' -delete
                find "$out" -type f -exec remove-references-to -t "$dev" {} +
                find "$lib" -name '*.la' -delete
                find "$lib" -type f -exec remove-references-to -t "$dev" {} +
+               find "$lib" -type f -exec remove-references-to -t "$out" {} +
              '';
            });
          });