Bug#897707: arrayfire FTBFS

[Rebecca N. Palmer]

Control: tags -1 patch

Taking just this part of the upstream patch (the other parts are for 
code our version doesn't have), together with the Boost fix (which I 
will file a separate bug for), makes it build.

Description: Fix const-related FTBFS with GCC 8

Author: Pradeep "9prady9"
Origin: upstream https://github.com/arrayfire/arrayfire/pull/2149
Bug-Debian: https://bugs.debian.org/897707

--- a/src/backend/cpu/blas.cpp
+++ b/src/backend/cpu/blas.cpp
@@ -157,8 +157,8 @@ Array<T> matmul(const Array<T> &lhs, con
      int aColDim = (lOpts == CblasNoTrans) ? 1 : 0;
      int bColDim = (rOpts == CblasNoTrans) ? 1 : 0;

-    dim4 lDims = lhs.dims();
-    dim4 rDims = rhs.dims();
+    auto lDims = lhs.dims();
+    auto rDims = rhs.dims();
      int M = lDims[aRowDim];
      int N = rDims[bColDim];
      int K = lDims[aColDim];