blas,lapack: use isILP64 instead of is64bit

This is a better name since we have multiple 64-bit things that could
be referred to.

LP64  : integer=32, long=64, pointer=64
ILP64 : integer=64, long=64, pointer=64

pkgs/development/libraries/science/math/superlu/default.nix

@@ -1,7 +1,7 @@
 { stdenv, fetchurl, cmake,
   gfortran, blas, lapack}:
 
-assert (!blas.is64bit) && (!lapack.is64bit);
+assert (!blas.isILP64) && (!lapack.isILP64);
 
 stdenv.mkDerivation rec {
   version = "5.2.1";