libpcap: Remove crossAttrs

pkgs/development/libraries/libpcap/default.nix

@@ -12,10 +12,16 @@ stdenv.mkDerivation rec {
 
   # We need to force the autodetection because detection doesn't
   # work in pure build enviroments.
-  configureFlags =
+  configureFlags = [
-    if stdenv.isLinux then [ "--with-pcap=linux" ]
+    ("--with-pcap=" + {
-    else if stdenv.isDarwin then [ "--with-pcap=bpf" ]
+      linux = "linux";
-    else [];
+      darwin = "bpf";
+    }.${stdenv.hostPlatform.parsed.kernel.name})
+  ] ++ stdenv.lib.optionals (stdenv.hostPlatform == stdenv.buildPlatform) [
+    "ac_cv_linux_vers=2"
+  ];
+
+  dontStrip = stdenv.hostPlatform != stdenv.buildPlatform;
 
   prePatch = stdenv.lib.optionalString stdenv.isDarwin ''
     substituteInPlace configure --replace " -arch i386" ""
@@ -39,12 +45,6 @@ stdenv.mkDerivation rec {
 
   preInstall = ''mkdir -p $out/bin'';
 
-  crossAttrs = {
-    # Stripping hurts in static libraries
-    dontStrip = true;
-    configureFlags = configureFlags ++ [ "ac_cv_linux_vers=2" ];
-  };
-
   meta = with stdenv.lib; {
     homepage = http://www.tcpdump.org;
     description = "Packet Capture Library";