vsftpd: fix cross-compilation, remove -Werror

pkgs/servers/ftp/vsftpd/default.nix

@@ -18,17 +18,18 @@ stdenv.mkDerivation rec {
     substituteInPlace Makefile \
       --replace -dirafter "" \
       --replace /usr $out \
-      --replace /etc $out/etc
+      --replace /etc $out/etc \
+      --replace "-Werror" ""
+
 
     mkdir -p $out/sbin $out/man/man{5,8}
   '';
 
-  NIX_LDFLAGS = "-lcrypt -lssl -lcrypto -lpam -lcap";
+  makeFlags = [
+    "CC=${stdenv.cc.targetPrefix}cc"
+  ];
 
-  # On gcc9, this would produce
-  #   error: '-Werror=enum-conversion': no option -Wenum-conversion
-  NIX_CFLAGS_COMPILE = lib.optionalString (lib.versionAtLeast stdenv.cc.version "10")
-    "-Wno-error=enum-conversion";
+  NIX_LDFLAGS = "-lcrypt -lssl -lcrypto -lpam -lcap";
 
   enableParallelBuilding = true;