wayland: Fix configure flag around cairo egl support

The intention was for this to default to off. However just using this option
(whether to enable or disable it) would turn it on.

Bugzilla: https://bugzilla.gnome.org/show_bug.cgi?id=688534

Thanks to Quentin Glidic for spotting this issue.

configure.ac

@@ -324,7 +324,8 @@ AC_ARG_ENABLE(quartz-relocation,
 AC_ARG_ENABLE(wayland-cairo-gl,
               AS_HELP_STRING([--enable-wayland-cairo-gl],
                              [enable the use of Cairo GL in the Wayland backend]),
-              [enable_wayland_cairo_gl=yes])
+              [],
+              [enable_wayland_cairo_gl=no])
 
 
 cairo_backends=