Re-enabled 2-stage diagonalization algorithms.

It seems that at some point, we renamed HAS_2STAGE to LAPACK_HAS_2STAGE within the CMake machinery, but we forgot to change the equivalence in the main CMakeLists and the one under Unfolding.

This renames the missing instances to re-enable those options.

Note: BACKPORT AFTER BAKCPORTING !247 (merged), just in case.