email: pull patch pending upstream inclusion for -fno-common toolchain supprot

Without the change build fails on upstream gcc-10 as:

    ld: utils.o:include/email.h:81: multiple definition of `Mopts'; email.o:include/email.h:81: first defined here
    ld: utils.o:include/email.h:64: multiple definition of `table'; email.o:include/email.h:64: first defined here
    ld: utils.o:include/email.h:65: multiple definition of `conf_file'; email.o:include/email.h:65: first defined here

pkgs/tools/networking/email/default.nix

@@ -1,4 +1,4 @@
-{ stdenv, lib, fetchFromGitHub, openssl }:
+{ stdenv, lib, fetchFromGitHub, fetchpatch, openssl }:
 
 let
   eMailSrc = fetchFromGitHub {
@@ -24,6 +24,16 @@ stdenv.mkDerivation {
   version = "unstable-2016-01-31";
   src = eMailSrc;
 
+  patches = [
+    # Pul patch pending upstream inclusion for -fno-common toolchain support:
+    #   https://github.com/deanproxy/eMail/pull/61
+    (fetchpatch {
+      name = "fno-common.patch";
+      url = "https://github.com/deanproxy/eMail/commit/c3c1e52132832be0e51daa6e0037d5bb79a17751.patch";
+      sha256 = "17ndrb65g0v4y521333h4244419s8nncm0yx2jwv12sf0dl6gy8i";
+    })
+  ];
+
   buildInputs = [ openssl ];
 
   unpackPhase = ''