dnsmasq: add optional DNSSEC support.

Closes Homebrew/homebrew#31204

Formula/dnsmasq.rb

@@ -12,8 +12,10 @@ class Dnsmasq < Formula
   end
 
   option 'with-idn', 'Compile with IDN support'
+  option 'with-dnssec', 'Compile with DNSSEC support'
 
   depends_on "libidn" if build.with? "idn"
+  depends_on "nettle" if build.with? "dnssec"
   depends_on 'pkg-config' => :build
 
   def install
@@ -27,6 +29,11 @@ class Dnsmasq < Formula
       inreplace "src/config.h", "/* #define HAVE_IDN */", "#define HAVE_IDN"
     end
 
+    # Optional DNSSEC support
+    if build.with? "dnssec"
+      inreplace "src/config.h", "/* #define HAVE_DNSSEC */", "#define HAVE_DNSSEC"
+    end
+
     # Fix compilation on Lion
     ENV.append_to_cflags "-D__APPLE_USE_RFC_3542" if MacOS.version >= :lion
     inreplace "Makefile" do |s|