fftw: use checkInputs, fix tests

pkgs/development/libraries/fftw/default.nix

@@ -1,4 +1,4 @@
-{ fetchurl, stdenv, lib, precision ? "double" }:
+{ fetchurl, stdenv, lib, precision ? "double", perl }:
 
 with lib;
 
@@ -38,6 +38,8 @@ stdenv.mkDerivation rec {
 
   enableParallelBuilding = true;
 
+  checkInputs = [ perl ];
+
   meta = with stdenv.lib; {
     description = "Fastest Fourier Transform in the West library";
     homepage = http://www.fftw.org/;