meson: Bump required meson version to 0.46

We were being naughty:

WARNING: Project specifies a minimum meson_version '>= 0.42.0' but uses features which were added in newer versions:
 * 0.46.0: {'compiler.has_multi_link_argument', 'compiler.has_link_argument'}

meson.build

@@ -4,7 +4,7 @@ project('xserver', 'c',
             'c_std=gnu99',
         ],
         version: '1.20.99.1',
-        meson_version: '>= 0.42.0',
+        meson_version: '>= 0.46.0',
 )
 add_project_arguments('-DHAVE_DIX_CONFIG_H', language: 'c')
 cc = meson.get_compiler('c')