meson: Set with_dri from with_gallium when DRI glx is explicitly configured

Set with_dri from with_gallium when DRI GLX is explicitly configured, as
well as when DRI GLX is chosen automatically.

Signed-off-by: Jon Turney <jon.turney@dronecode.org.uk>
Reviewed-by: Dylan Baker <dylan@pnwbakers.com>

meson.build

@@ -248,7 +248,6 @@ if with_glx == 'auto'
   elif with_gallium
     # Even when building just gallium drivers the user probably wants dri
     with_glx = 'dri'
-    with_dri = true
   elif with_platform_x11 and with_any_opengl and not with_any_vk
     # The automatic behavior should not be to turn on xlib based glx when
     # building only vulkan drivers
@@ -257,6 +256,11 @@ if with_glx == 'auto'
     with_glx = 'disabled'
   endif
 endif
+if with_glx == 'dri'
+   if with_gallium
+      with_dri = true
+   endif
+endif
 
 if not (with_dri or with_gallium or with_glx == 'xlib' or with_glx == 'gallium-xlib')
   with_gles1 = false