john: use gcc 4.9 instead of 5 (unbreaks build)

Fixes this build error:

  dynamic_fmt.o: In function `DynamicFunc__crypt_md5_to_input_raw_Overwrite_NoLen':
  .../john-1.8.0-jumbo-1/src/dynamic_fmt.c:4989: undefined reference to `MD5_body_for_thread'

Upstream issue:

  openwall/john#1093

pkgs/tools/security/john/default.nix

@@ -1,5 +1,5 @@
 { stdenv, fetchurl, openssl, nss, nspr, kerberos, gmp, zlib, libpcap, re2
-, writeText
+, writeText, gcc
 }:
 
 with stdenv.lib;
@@ -27,7 +27,7 @@ stdenv.mkDerivation rec {
   preConfigure = "cd src";
   configureFlags = [ "--disable-native-macro" ];
 
-  buildInputs = [ openssl nss nspr kerberos gmp zlib libpcap re2 ];
+  buildInputs = [ openssl nss nspr kerberos gmp zlib libpcap re2 gcc ];
   enableParallelBuilding = true;
 
   NIX_CFLAGS_COMPILE = [ "-DJOHN_SYSTEMWIDE=1" ];

pkgs/top-level/all-packages.nix

@@ -2101,7 +2101,9 @@ in
 
   jnettop = callPackage ../tools/networking/jnettop { };
 
-  john = callPackage ../tools/security/john { };
+  john = callPackage ../tools/security/john {
+    gcc = gcc49; # doesn't build with gcc5
+  };
 
   jp2a = callPackage ../applications/misc/jp2a { };