meson: allow building all glx without any drivers

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=111016
Fixes: a47c525f32
       ("meson: build glx")
Acked-by: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Eric Anholt <eric@anholt.net>

meson.build

@@ -315,7 +315,7 @@ if with_glx == 'dri'
    endif
 endif
 
-if not (with_dri or with_gallium or with_glx == 'xlib' or with_glx == 'gallium-xlib')
+if not (with_dri or with_gallium or with_glx != 'disabled')
   with_gles1 = false
   with_gles2 = false
   with_opengl = false
@@ -382,9 +382,7 @@ if with_glx != 'disabled'
       error('xlib conflicts with any dri driver')
     endif
   elif with_glx == 'dri'
-    if not with_dri
-      error('dri based GLX requires at least one DRI driver')
-    elif not with_shared_glapi
+    if not with_shared_glapi
       error('dri based GLX requires shared-glapi')
     endif
   endif

src/glx/meson.build

@@ -1,4 +1,4 @@
-# Copyright © 2017 Intel Corporation
+# Copyright © 2017-2019 Intel Corporation
 
 # Permission is hereby granted, free of charge, to any person obtaining a copy
 # of this software and associated documentation files (the "Software"), to deal
@@ -70,7 +70,7 @@ extra_libs_libglx = []
 extra_deps_libgl = []
 extra_ld_args_libgl = []
 
-if with_dri
+if with_glx == 'dri'
   files_libglx += files(
     'dri_common.c',
     'dri_common.h',
@@ -83,7 +83,7 @@ if with_dri
 endif
 
 # dri2
-if with_dri and with_dri_platform == 'drm' and dep_libdrm.found()
+if with_glx == 'dri' and with_dri_platform == 'drm' and dep_libdrm.found()
   files_libglx += files(
     'dri2.c',
     'dri2_glx.c',