BLAS: Does cblas interface work with BLAS types other than netlib

[Mayuresh <mayuresh%acm.org@localhost>]

This on NetBSD 9.2 amd64, a few weeks old pkgsrc.

In wip/dlib-cpp I am trying to use BLAS by including blas.buildlink3.mk

By default it selects netlib implementation and there is no error by
package's configurator.

However as blas.buildlink3.mk  documentation says, it is one of the
slowest implementations. So, if I select any other implementation the
package configurator gives the following error:

    -- BLAS library does not have cblas symbols, so dlib will not use BLAS or LAPACK

Even if I add the following, above error doesn't go away.

    BLAS_C_INTERFACE=       yes

So it appears that BLAS_C_INTERFACE works only with the netlib option. But
if that was the case why would blas.buildlink3.ml document it as a package
settable variable?

Can someone please throw some light on this?

-- 
Mayuresh