meson: Don't allow glx to be built without platform_x11

Previously this failed to change with_glx to disabled from auto if
platform_x11 was unset or if no opengl apis were being built.

v2: - swap conditional positions

Signed-off-by: Dylan Baker <dylanx.c.baker@intel.com>
Reviewed-and-Tested-by: Eric Engestrom <eric@engestrom.ch>
1 file changed