targets/dri: resolve the scons build

With earlier commit we've conditionally enabled/added the kms_dri target
for automake builds. Unfortunately the we forgot to add the appropriate
define in the scons build, resulting in a broken library due to the
undefined symbol 'kms_swrast_create_screen'.

Reported-by: Roland Scheidegger <sroland@vmware.com>
Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>
Tested-by: Roland Scheidegger <sroland@vmware.com>

src/gallium/targets/dri/SConscript

@@ -29,6 +29,7 @@ env.Append(CPPDEFINES = [
     'GALLIUM_VMWGFX',
     'GALLIUM_SOFTPIPE',
     'DRI_TARGET',
+    'HAVE_LIBDRM',
 ])
 
 env.Prepend(LIBS = [