Added Lapack in linalg.h and a fixed a minor #elif.

From lapack 2 dot product methods have been used ie cblas_ddot and cblas_sdot in shogun and also the arguments taken by these methods are different than that for the eigen3 dot methods. How can we express these 2 as static T compute( , ) so that all dot product calls can be replace by single compute method without any guards?
I thought the way i implemented was correct but later i understood the whole picture of whats really to be done.