Add ext-comp-refs dependency on ext-refs in configure

This will remove the compilation failure for the weekly run on speed
checking.

Change-Id: Idf688c7e4c6fcb4c5aabef68b0e9f68996cd9a12

configure

diff --git a/configure b/configure
index 0093007..f4c509a 100755
--- a/configure
+++ b/configure
@@ -554,6 +554,7 @@
     enabled warped_motion && disable_feature ncobmc_adapt_weight
     enabled ncobmc_adapt_weight && enable_feature motion_var
     enabled bgsprite && enable_feature global_motion
+    enabled ext_comp_refs && enable_feature ext_refs
     enabled ext_comp_refs && enable_feature var_refs
     enabled ext_comp_refs && disable_feature one_sided_compound
     enabled altref2 && enable_feature ext_refs