[SCons] Fix a problem with Cantera.mak and user-provided BLAS/LAPACK

All cases need to define the mak_blas_lapack_libs_dep variable that
was introduced in r2535.

git-svn-id: https://cantera.googlecode.com/svn/cantera/trunk@2563 02a645c2-efd0-11dd-984d-ab748d24aa7e