With USE=-X, do not enable X11 based on the build host's installed libraries.
The ebuild applies this patch only when X is disabled; USE=X retains upstream
probing and the explicit libX11 dependencies for SDL/GTK.

See: https://github.com/gentoo/gentoo/commit/59de979e86be868bf5985b39cd1be55b20c75f89

--- a/meson.build
+++ b/meson.build
@@ -1940,7 +1940,7 @@
   endif
 endif
 
-x11 = dependency('x11', method: 'pkg-config', required: gtkx11.found())
+x11 = not_found
 
 png = not_found
 if get_option('png').allowed() and have_system