build with Meson instead of autotools

So long, autotools!  This is my last MPD related project to migrate
away from it.  It has its strengths, but also very obvious weaknesses
and weirdnesses.  Today, many of its quirks are not needed anymore,
and are cumbersome and slow.  Now welcome our new Meson overlords!

src/zeroconf/meson.build

@@ -0,0 +1,74 @@
+zeroconf_option = get_option('zeroconf')
+
+libavahi_client_dep = dependency('', required: false)
+
+if zeroconf_option == 'auto'
+  if is_darwin
+    # Bonjour disabled for now because its build is broken
+    #zeroconf_option = 'bonjour'
+    zeroconf_option = 'disabled'
+  elif is_android or is_windows
+    zeroconf_option = 'disabled'
+  elif dbus_dep.found()
+    libavahi_client_dep = dependency('avahi-client', required: false)
+    if libavahi_client_dep.found()
+      zeroconf_option = 'avahi'
+    else
+      zeroconf_option = 'disabled'
+    endif
+  else
+    zeroconf_option = 'disabled'
+  endif
+endif
+
+if zeroconf_option == 'disabled'
+  zeroconf_dep = dependency('', required: false)
+  subdir_done()
+endif
+
+if zeroconf_option == 'bonjour'
+  if not compiler.has_header('dns_sd.h')
+    error('dns_sd.h not found')
+  endif
+  
+  bonjour_dep = declare_dependency(link_args: ['-framework', 'dnssd'])
+  conf.set('HAVE_BONJOUR', true)
+  
+  zeroconf = static_library(
+    'zeroconf_bonjour',
+    'ZeroconfGlue.cxx',
+    'ZeroconfBonjour.cxx',
+    include_directories: inc,
+  )
+
+  zeroconf_dep = declare_dependency(
+    link_with: zeroconf,
+    dependencies: [
+      bonjour_dep,
+    ],
+  )
+else
+  if not libavahi_client_dep.found()
+    libavahi_client_dep = dependency('avahi-client')
+  endif
+
+  conf.set('HAVE_AVAHI', true)
+  
+  zeroconf = static_library(
+    'zeroconf_bonjour',
+    'ZeroconfGlue.cxx',
+    'ZeroconfAvahi.cxx',
+    'AvahiPoll.cxx',
+    include_directories: inc,
+    dependencies: [
+      libavahi_client_dep,
+      dbus_dep,
+    ],
+  )
+
+  zeroconf_dep = declare_dependency(
+    link_with: zeroconf,
+  )
+endif
+
+conf.set('HAVE_ZEROCONF', true)