Find{BLAS,LAPACK}: improve found message on Cray and clean side effects
With Cray compiler wrappers (tested on OLCF Spock) the BLAS and LAPACK libraries are automatically linked as necessary through the wrapper script and programming environment. With this change, the configure output is:
-- Found BLAS: implicitly linked
<snip>
-- Found LAPACK: implicitly linked
rather than
-- Found BLAS: 1
<snip>
-- Found LAPACK: LAPACK_LIBRARIES-PLACEHOLDER-FOR-EMPTY-LIBRARIES
(details)
Additionally, clean a number of incidental variables that are not unset in the packages (details)