message: lock down spack by commit
diff: "package_final_phase": "initconfig",
  "package_source_dir": "../..",
  "spack_url": "https://github.com/spack/spack",
  -"spack_branch": "features/cached-cmake-build-system",
  +"spack_commit": "764c17053041a65f684ce565a2598d705b04a16b",
  "spack_configs_path": "scripts/spack/configs",
  "spack_packages_path": "scripts/spack/packages",
  "vcpkg_url": "https://github.com/microsoft/vcpkg",
  