meson: make GLX require OpenGL

This isn't strictly true, but making that work isn't worth the effort;
see https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/21343#note_1774683

Suggested-by: Adam Jackson <ajax@redhat.com>
Signed-off-by: Eric Engestrom <eric@igalia.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/21343>

meson.build

@@ -320,7 +320,9 @@ with_platform_windows = _platforms.contains('windows')
 
 with_glx = get_option('glx')
 if with_glx == 'auto'
-  if with_platform_android
+  if not with_opengl
+    with_glx = 'disabled'
+  elif with_platform_android
     with_glx = 'disabled'
   elif with_dri
     with_glx = 'dri'
@@ -345,6 +347,10 @@ if with_glx == 'dri'
    endif
 endif
 
+if not with_opengl and with_glx != 'disabled'
+  error('Building GLX without OpenGL is not supported.') \
+endif
+
 if not (with_dri or with_gallium or with_glx != 'disabled')
   with_gles1 = false
   with_gles2 = false