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/qrupdate/default.nix

@@ -18,7 +18,7 @@ stdenv.mkDerivation {
           -e 's,^LAPACK=.*,LAPACK=-L${lapack}/lib -llapack,' \
           Makeconf
     ''
-    + stdenv.lib.optionalString blas.is64bit
+    + stdenv.lib.optionalString blas.isILP64
     ''
       sed -i Makeconf -e '/^FFLAGS=.*/ s/$/-fdefault-integer-8/'
     '';