build: check for cvt only when building the native backend

Also error out properly when cvt is not found on Autotools.

configure.ac

@@ -430,9 +430,11 @@ AC_CHECK_DECL([GL_EXT_x11_sync_object],
               [AC_MSG_ERROR([GL_EXT_x11_sync_object definition not found, please update your GL headers])],
               [#include <GL/glx.h>])
 
-AC_PATH_PROG([CVT],[cvt],[])
+if test "$have_native_backend" = yes; then
-if test x"$CVT" = xno; then
+  AC_PATH_PROG([CVT],[cvt],[])
-  AC_MSG_ERROR([cvt not found in your path])
+  if test x"$CVT" = x; then
+    AC_MSG_ERROR([cvt not found in your path])
+  fi
 fi
 
 #### Warnings (last since -Werror can disturb other tests)

src/meson.build

@@ -583,6 +583,15 @@ dbus_idle_monitor_built_sources = gnome.gdbus_codegen('meta-dbus-idle-monitor',
 mutter_built_sources += dbus_idle_monitor_built_sources
 
 if have_native_backend
+  cvt = find_program('cvt')
+
+  gen_default_modes = find_program('backends/native/gen-default-modes.py')
+  default_modes_h = custom_target('meta-default-modes',
+    output: 'meta-default-modes.h',
+    command: [gen_default_modes, '@OUTPUT@']
+  )
+  mutter_built_sources += default_modes_h
+
   gdbus_codegen = find_program('gdbus-codegen')
   dbus_login1_built_sources = custom_target('meta-dbus-login1',
     input: 'org.freedesktop.login1.xml',
@@ -619,15 +628,6 @@ if have_remote_desktop
   mutter_built_sources += dbus_screen_cast_built_sources
 endif
 
-cvt = find_program('cvt')
-
-gen_default_modes = find_program('backends/native/gen-default-modes.py')
-default_modes_h = custom_target('meta-default-modes',
-  output: 'meta-default-modes.h',
-  command: [gen_default_modes, '@OUTPUT@']
-)
-mutter_built_sources += default_modes_h
-
 if have_wayland
   # Format:
   #  - protocol name