Support to run DroidDoc in unbundled builds.

Change-Id: Ia5ace10ed75c451e346e289f0c534ad619abdb65
diff --git a/core/Makefile b/core/Makefile
index 169fc02..11a897a 100644
--- a/core/Makefile
+++ b/core/Makefile
@@ -38,11 +38,13 @@
 
 # -----------------------------------------------------------------
 # docs/index.html
+ifeq (,$(TARGET_BUILD_APPS))
 gen := $(OUT_DOCS)/index.html
 ALL_DOCS += $(gen)
 $(gen): frameworks/base/docs/docs-redirect-index.html
 	@mkdir -p $(dir $@)
 	@cp -f $< $@
+endif
 
 # -----------------------------------------------------------------
 # default.prop