igraph doesn't build on some systems:

[igraph-0.7.1999] /usr/lib/gcc/x86_64-pc-linux-gnu/4.9.3/../../../../x86_64-pc-linux-gnu/bin/ld: cannot find -lblas
[igraph-0.7.1999] /usr/lib/gcc/x86_64-pc-linux-gnu/4.9.3/../../../../x86_64-pc-linux-gnu/bin/ld: cannot find -llapack

Ideally, it should use OpenBLAS but it doesn't. Note that linking against OpenBLAS should be done with -lopenblas, not -lblas.

The use of blas/lapack in the (new) igraph is optional, so we just not use them in this branch.

We also specify the required in the (new) igraph package glpk in its dependencies.

CC: @dimpase

Component: packages: optional

Author: Dima Pasechnik

Branch/Commit: 28d375f

Reviewer: Jeroen Demeyer

Issue created by migration from https://trac.sagemath.org/ticket/27597