meson: Print some configure flags

Just an additional touch after adding installed tests,
outputting those flags helped not losing track of them.

meson.build

@@ -327,3 +327,47 @@ subdir('data')
 subdir('src')
 subdir('po')
 subdir('doc/man')
+
+output = [
+  '',
+  '',
+  '   Mutter ' + meson.project_version(),
+  '  ===============',
+  '',
+  '    Prefix....................... ' + prefix,
+  '    libexecdir................... ' + libexecdir,
+  '    pkgdatadir................... ' + pkgdatadir,
+  '',
+  '    Rendering APIs:',
+  '',
+  '        OpenGL................... ' + have_gl.to_string(),
+  '        GLES2.................... ' + have_gles2.to_string(),
+  '        EGL...................... ' + have_egl.to_string(),
+  '        GLX...................... ' + have_glx.to_string(),
+  '',
+  '    Options:',
+  '',
+  '        Wayland.................. ' + have_wayland.to_string(),
+  '        Wayland EGLStream........ ' + have_wayland.to_string(),
+  '        Native Backend........... ' + have_native_backend.to_string(),
+  '        EGL Device............... ' + have_egl_device.to_string(),
+  '        Remote desktop........... ' + have_remote_desktop.to_string(),
+  '        gudev.................... ' + have_libgudev.to_string(),
+  '        canberra................. ' + have_libcanberra.to_string(),
+  '        Wacom.................... ' + have_libwacom.to_string(),
+  '        SM....................... ' + have_sm.to_string(),
+  '        Startup notification..... ' + have_startup_notification.to_string(),
+  '        Introspection............ ' + have_introspection.to_string(),
+  '',
+  '    Tests:',
+  '',
+  '        Enabled.................. ' + have_tests.to_string(),
+  '        Cogl tests............... ' + have_cogl_tests.to_string(),
+  '        Clutter tests............ ' + have_clutter_tests.to_string(),
+  '        Installed tests.......... ' + have_installed_tests.to_string(),
+  '',
+  '  Now type \'ninja -C ' + meson.build_root() + '\' to build ' + meson.project_name(),
+  '',
+  '',
+]
+message('\n'.join(output))