[gtk+] build: Add Meson options for quartz/win32 backends

[Emmanuele Bassi <ebassi src gnome org>]

commit 6b4b3f2f6cee3a2067972a0d4f6bf4a816323576
Author: Emmanuele Bassi <ebassi gnome org>
Date:   Wed Apr 26 15:15:45 2017 +0100

    build: Add Meson options for quartz/win32 backends

 meson_options.txt |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)
---
diff --git a/meson_options.txt b/meson_options.txt
index f9a419d..55ea538 100644
--- a/meson_options.txt
+++ b/meson_options.txt
@@ -8,6 +8,10 @@ option('enable-broadway-backend', type: 'boolean', value: 'false',
   description : 'Enable the broadway (HTML5) gdk backend')
 option('enable-mir-backend', type: 'boolean', value: 'false',
   description : 'Enable the Mir gdk backend (UNTESTED, NEEDS WORK)')
+option('enable-win32-backend', type: 'boolean', value: 'false',
+  description : 'Enable the Windows gdk backend')
+option('enable-quartz-backend', type: 'boolean', value: 'false',
+  description : 'Enable the macOS gdk backend')
 option('enable-vulkan', type: 'combo', choices : ['yes', 'no', 'auto'], value : 'auto',
   description : 'Enable support for the Vulkan graphics API')
 option('enable-test-print-backend', type: 'combo', choices : ['yes', 'no', 'auto'], value : 'no',