Fix postgresql-musl: merge dev into out to eliminate dev↔lib cycle

The postgresql musl cross-build fails with:
  error: cycle detected in build of '...-postgresql-musl-17.7.drv'
  in the references of output 'dev' from output 'lib'

The lib output (shared libraries) contains baked-in references to
the dev output path, while dev naturally references lib. The
remove-references-to approach didn't resolve it (references may be
in ELF sections or .rodata that survive stripping).

Instead, merge dev into out by removing "dev" from outputs. When
"dev" is absent from outputs, $dev defaults to $out, so headers and
pkgconfig files end up in $out. Downstream packages using
postgresql.dev get postgresql.out (default output for missing output
names). This eliminates the cycle entirely.

Author: angerman

flake.nix

@@ -170,32 +170,15 @@
                NIX_CFLAGS_COMPILE = (old.env.NIX_CFLAGS_COMPILE or "") + " -fno-lto";
              };
              doCheck = false;
+             # Merge dev into out to eliminate the dev↔lib reference cycle.
+             # When "dev" is removed from outputs, $dev defaults to $out,
+             # so all headers/pkgconfig files end up in $out. Downstream
+             # packages using postgresql.dev get postgresql.out (default
+             # output behavior for missing outputs).
+             outputs = prev.lib.remove "dev" (old.outputs or [ "out" ]);
              outputChecks = {};
              separateDebugInfo = false;
              disallowedReferences = [];
-             # Break the dev↔lib reference cycle: dev naturally references
-             # lib (via .pc -L flags), but lib also picks up dev references
-             # through .la files and baked-in paths. Strip dev refs from lib
-             # since lib is a runtime output that doesn't need dev at runtime.
-             postFixup = (old.postFixup or "") + ''
-               echo "=== postFixup: stripping dev refs from lib ==="
-               echo "lib=$lib"
-               echo "dev=$dev"
-               echo "Files in lib:"
-               find "$lib" -type f | head -20
-               # Delete .la files from lib — libtool archives embed absolute
-               # paths to dev headers/libs and are unnecessary for runtime.
-               find "$lib" -name '*.la' -delete
-               # Check which files in lib reference dev before stripping.
-               echo "Files in lib referencing dev hash:"
-               DEV_HASH=$(echo "$dev" | sed 's|/nix/store/||; s|-.*||')
-               grep -rl "$DEV_HASH" "$lib" 2>/dev/null || echo "  (none found)"
-               # Strip any remaining references to $dev from the lib output.
-               find "$lib" -type f -exec remove-references-to -t "$dev" {} +
-               echo "After stripping, files referencing dev hash:"
-               grep -rl "$DEV_HASH" "$lib" 2>/dev/null || echo "  (none found)"
-               echo "=== postFixup done ==="
-             '';
            });
          });
        };