octave: build with openblas

The expression inherits integer width from OpenBLAS, so Octave will use
64-bit integers if OpenBLAS supports it. However, this feature in Octave
is experimental, so we continue to use OpenBLAS with 32-bit integers by
default. (This only applies to the integer width, the pointer width is
always the platform-native width.)

pkgs/development/interpreters/octave/default.nix

···
 { stdenv, fetchurl, gfortran, readline, ncurses, perl, flex, texinfo, qhull
-, libX11, graphicsmagick, pcre, liblapack, pkgconfig, mesa, fltk
-, fftw, fftwSinglePrec, zlib, curl, qrupdate
+, libX11, graphicsmagick, pcre, pkgconfig, mesa, fltk
+, fftw, fftwSinglePrec, zlib, curl, qrupdate, openblas
 , qt ? null, qscintilla ? null, ghostscript ? null, llvm ? null, hdf5 ? null,glpk ? null
 , suitesparse ? null, gnuplot ? null, jdk ? null, python ? null
 }:
 
+let
+  suitesparseOrig = suitesparse;
+  qrupdateOrig = qrupdate;
+in
+# integer width is determined by openblas, so all dependencies must be built
+# with exactly the same openblas
+let
+  suitesparse =
+    if suitesparseOrig != null then suitesparseOrig.override { inherit openblas; } else null;
+  qrupdate = if qrupdateOrig != null then qrupdateOrig.override { inherit openblas; } else null;
+in
+
 stdenv.mkDerivation rec {
   version = "4.0.0";
   name = "octave-${version}";
···
   };
 
   buildInputs = [ gfortran readline ncurses perl flex texinfo qhull libX11
-    graphicsmagick pcre liblapack pkgconfig mesa fltk zlib curl
+    graphicsmagick pcre pkgconfig mesa fltk zlib curl openblas
     fftw fftwSinglePrec qrupdate ]
     ++ (stdenv.lib.optional (qt != null) qt)
     ++ (stdenv.lib.optional (qscintilla != null) qscintilla)
···
   # problems on Hydra
   enableParallelBuilding = false;
 
-  configureFlags = [ "--enable-readline" "--enable-dl" ];
+  configureFlags =
+    [ "--enable-readline"
+      "--enable-dl"
+      "--with-blas=openblas"
+      "--with-lapack=openblas"
+    ]
+    ++ stdenv.lib.optional openblas.blas64 "--enable-64";
 
   # Keep a copy of the octave tests detailed results in the output
   # derivation, because someone may care

pkgs/top-level/all-packages.nix

···
     glpk = null;
     suitesparse = null;
     jdk = null;
+    openblas = openblasCompat;
   };
   octaveFull = (lowPrio (callPackage ../development/interpreters/octave {
     fltk = fltk13.override { cfg.xftSupport = true; };