Fix postgresql musl: disable separateDebugInfo to prevent GC race

The postgresql musl cross-build completes all phases successfully
(buildPhase, installPhase, fixupPhase) but the outputs get garbage
collected by the builder's min-free auto-GC before they can be
transferred back to the hydra machine. The massive -debug output
(hundreds of debug symlinks) makes the nix-copy transfer too slow.

Disable separateDebugInfo to eliminate the -debug output entirely,
reducing transfer size and avoiding the GC race.

Both x86_64-musl (16 attempts on darwin-7) and aarch64-musl (6
attempts on darwin-6) exhibited this pattern: build log shows all
phases completing but outputs are absent from both builder and
hydra stores.

Author: angerman

flake.nix

@@ -155,6 +155,12 @@
              };
              doCheck = false;
              outputChecks = {};
+             # Disable separateDebugInfo to avoid massive -debug output
+             # with hundreds of symlinks. The debug output size causes
+             # nix-copy transfers to take too long, racing against the
+             # builder's min-free auto-GC which deletes the outputs
+             # before they can be transferred to the hydra machine.
+             separateDebugInfo = false;
            });
          });
        };