Specify "Generic" BLAS library name. (#74269)
When we use pytorch with unregistered blas, spack set BLAS=Generic.
pytorch is searched only libblas.
If the blas package's blas library name is not libblas, spack install py-torch is failed.
This PR set blas lirary names to GENERIC_BLAS_LIBRARIES environment variable, and py-torch is found blas library.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/74269
Approved by: https://github.com/kit1980
