lean4, leanPackages.lean4: fix darwin build by adding libtool
Lake 4.30.0 uses libtool -static on macOS for static library targets
instead of ar.
https://github.com/leanprover/lean4/blob/d024af099ca4bf2c86f649261ebf59565dc8c622/src/lake/Lake/Build/Library.lean#L87-L95
See Hydra Build No. 330752454, lean4.aarch64-darwin (June 4, 2026),
https://hydra.nixos.org/build/330752454; Hydra Build No. 330752481,
leanPackages.lean4.aarch64-darwin (June 4, 2026),
https://hydra.nixos.org/build/330752481.
Breakage introduced in
https://github.com/NixOS/nixpkgs/pull/526718/commits/a26b66330f6fa572e7005ee2a1eb031093456e6e
Nadja Yang
03752ca7ca