ncrack: pull upstream fix for fno-common toolchains

Without the change build on -fno-common toolchains like upstream gcc-10
fails as:

    $ nix build -L --impure --expr 'with import ./. {}; ncrack.overrideAttrs (oa: {   NIX_CFLAGS_COMPILE = (oa.NIX_CFLAGS_COMPILE or "") + "-fno-common"; })'
    ...
    ld: opensshlib/libopenssh.a(umac128.o):/build/source/opensshlib/umac.c:1184:
      multiple definition of `umac_ctx'; opensshlib/libopenssh.a(umac.o):/build/source/opensshlib/umac.c:1184: first defined here

pkgs/tools/security/ncrack/default.nix

@@ -1,4 +1,4 @@
-{ lib, stdenv, fetchFromGitHub, openssl, zlib }:
+{ lib, stdenv, fetchFromGitHub, fetchpatch, openssl, zlib }:
 
 stdenv.mkDerivation rec {
   pname = "ncrack";
@@ -11,6 +11,16 @@ stdenv.mkDerivation rec {
     sha256 = "1gnv5xdd7n04glcpy7q1mkb6f8gdhdrhlrh8z6k4g2pjdhxlz26g";
   };
 
+  patches = [
+    # Pull upstream fix for -fno-common toolchains like upstream gcc-10:
+    #   https://github.com/nmap/ncrack/pull/83
+    (fetchpatch {
+      name = "fno-common.patch";
+      url = "https://github.com/nmap/ncrack/commit/cc4103267bab6017a4da9d41156d0c1075012eba.patch";
+      sha256 = "06nlfvc7p108f8ppbcgwmj4iwmjy95xhc1sawa8c78lrx22r7gy3";
+    })
+  ];
+
   buildInputs = [ openssl zlib ];
 
   meta = with lib; {