Commit patch sent by Sébastien Fabbro to enable LAPACKE built without LAPACK.

Commit patch sent by Sébastien Fabbro to enable LAPACKE built without LAPACK.
The patch has been modified a little by Julie as there were some minors problems.
This also fix the BUILD_TESTING=OFF option problem reported by Marcin on lapack mailing list.

From Sébastien:
Here is a patch to compile lapacke with CMake using an already
existing optimized lapack library instead of forcing the build of the
included one in the tar ball. It applies to the latest lapack svn
trunk.