meson: make Xext a mandatory dep

As XSHM is mandatory we can no longer build without
Xext, so tidy up the build code.

Signed-off-by: Matt Jolly <kangie@gentoo.org>

meson.build

@@ -188,6 +188,10 @@ foreach rd : all_req_deps
     all_found_deps += this_dep
 endforeach
 
+xext = dependency('xext', required: true)
+all_found_deps += xext
+conf.set10('SHAPE', true)
+
 # Python is a required dependency, we generate shebangs at buildtime
 # This will error by default if there is no python interpreter found
 py_mod = import('python')
@@ -335,12 +339,6 @@ if xcursor.found()
     conf.set10('HAVE_XCURSOR', true)
 endif
 
-xext = dependency('xext', required: get_option('xext'))
-if xext.found()
-    all_found_deps += xext
-    conf.set10('SHAPE', true)
-endif
-
 xkbcommon = dependency('xkbcommon', required: get_option('xkbcommon'))
 if xkbcommon.found()
     all_found_deps += xkbcommon

meson.options

@@ -88,12 +88,6 @@ option(
     value: 'auto',
     description: 'Enable Xcursor support',
 )
-option(
-    'xext',
-    type: 'feature',
-    value: 'auto',
-    description: 'Enable shaped window support via Xext',
-)
 option(
     'xkbcommon',
     type: 'feature',