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/top-level/release-alternatives.nix

@@ -59,7 +59,7 @@ in
 {
   blas = mapListToAttrs supportedSystems (system': let system = lib.systems.elaborate { system = system'; };
     in mapListToAttrs (blasProviders system) (provider: let
-      is64bit = builtins.elem provider (["mkl64"] ++ lib.optional system.is64bit "openblas");
+      isILP64 = builtins.elem provider (["mkl64"] ++ lib.optional system.is64bit "openblas");
       pkgs = pkgsFun {
         config = { inherit allowUnfree; };
         system = system';
@@ -68,13 +68,13 @@ in
             lapackProvider = if provider == "mkl64"
                              then super.mkl
                              else builtins.getAttr provider super;
-            inherit is64bit;
+            inherit isILP64;
           };
           blas = super.blas.override {
             blasProvider = if provider == "mkl64"
                            then super.mkl
                            else builtins.getAttr provider super;
-            inherit is64bit;
+            inherit isILP64;
           };
         })];
       };