build: Replace Autotools with Meson

Quick rundown of benefits:

- Much faster:
  - Autotools (with autogen): 22 seconds
  - Meson: 7 seconds
  - Meson (with ccache): 2 seconds

- Simpler:
  - ~1000 lines smaller
  - Single simple language

- Potentially better Windows (Visual Studio) support

What is not done:

- Complete Windows support
- OSX support (easy)

Closes #2013
Closes #1937
Closes #1803

src/fe-gtk/meson.build

@@ -0,0 +1,79 @@
+hexchat_gtk_sources = [
+  'ascii.c',
+  'banlist.c',
+  'chanlist.c',
+  'chanview.c',
+  'custom-list.c',
+  'dccgui.c',
+  'editlist.c',
+  'fe-gtk.c',
+  'fkeys.c',
+  'gtkutil.c',
+  'ignoregui.c',
+  'joind.c',
+  'menu.c',
+  'maingui.c',
+  'notifygui.c',
+  'palette.c',
+  'pixmaps.c',
+  'plugin-tray.c',
+  'plugin-notification.c',
+  'rawlog.c',
+  'servlistgui.c',
+  'setup.c',
+  'sexy-spell-entry.c',
+  'textgui.c',
+  'urlgrab.c',
+  'userlistgui.c',
+  'xtext.c'
+]
+
+hexchat_gtk_deps = [
+  hexchat_common_dep,
+  libgmodule_dep, # used by libsexy
+  dependency('gtk+-2.0', version: '>= 2.24.0')
+]
+
+hexchat_gtk_cflags = [
+  '-fPIE'
+]
+
+hexchat_gtk_ldflags = [
+  '-pie'
+]
+
+if get_option('with-libnotify')
+  hexchat_gtk_sources += 'notifications/notification-libnotify.c'
+  hexchat_gtk_deps += dependency('libnotify')
+elif false # TODO HAVE_GTK_MAC
+else
+  hexchat_gtk_sources += 'notifications/notification-dummy.c'
+endif
+
+iso_codes = dependency('iso-codes', required: false)
+if iso_codes.found()
+  hexchat_gtk_sources += 'sexy-iso-codes.c'
+  iso_codes_prefix = iso_codes.get_pkgconfig_variable('prefix')
+  hexchat_gtk_cflags += '-DISO_CODES_PREFIX="@0@"'.format(iso_codes_prefix)
+  hexchat_gtk_cflags += '-DISO_CODES_LOCALEDIR="@0@"'.format(
+                        join_paths(iso_codes_prefix, 'share/locale'))
+endif
+
+if get_option('with-plugin')
+  hexchat_gtk_sources += 'plugingui.c'
+endif
+
+resources = gnome.compile_resources('resources',
+  '../../data/hexchat.gresource.xml',
+  source_dir: '../../data', # TODO: Fix upstream
+  c_name: 'hexchat',
+  extra_args: ['--manual-register']
+)
+
+executable('hexchat',
+  sources:  resources + hexchat_gtk_sources,
+  dependencies: hexchat_gtk_deps,
+  c_args: hexchat_gtk_cflags,
+  link_args: hexchat_gtk_ldflags,
+  install: true
+)