lapacke_64.h does not get installed

[grisuthedragon]

Description

When building LAPACK with the EXT_64API and including LAPACKE, the lapacke_64.h does not get installed.

For example if I include LAPACKE using

#define LAPACKE_API
#include <lapacke.h> 

or

#include <lapacke_64.h> 

The file gets not found in an installed LAPACK.

Searching for lapacke_64.h in the sources does not give any point where it is connected to a make install target.

• [x] I've included a minimal example to reproduce the issue
• [x] I'd be willing to make a PR to solve this issue, once I have time.