Make the recovery.img construction (from boot.img) logic depend on whether recovery.img was installed.
Don't have to re-specify exclusion list for the patch file construction.
diff --git a/core/Makefile b/core/Makefile
index 27e3eac..9247c75 100644
--- a/core/Makefile
+++ b/core/Makefile
@@ -646,8 +646,7 @@
 # as the source (since they are very similar).  Generate the patch so
 # we can see how big it's going to be, and include that in the system
 # image size check calculation.
-ifneq ($(TARGET_PRODUCT),sdk)
-ifneq ($(TARGET_PRODUCT),generic)
+ifneq ($(INSTALLED_RECOVERYIMAGE_TARGET),)
 intermediates := $(call intermediates-dir-for,PACKAGING,recovery_patch)
 RECOVERY_FROM_BOOT_PATCH := $(intermediates)/recovery_from_boot.p
 $(RECOVERY_FROM_BOOT_PATCH): $(INSTALLED_RECOVERYIMAGE_TARGET) \
@@ -657,8 +656,8 @@
 	@echo "Construct recovery from boot"
 	mkdir -p $(dir $@)
 	PATH=$(HOST_OUT_EXECUTABLES):$$PATH $(HOST_OUT_EXECUTABLES)/imgdiff $(INSTALLED_BOOTIMAGE_TARGET) $(INSTALLED_RECOVERYIMAGE_TARGET) $@
-endif  # TARGET_PRODUCT != generic
-endif  # TARGET_PRODUCT != sdk
+endif
+
 
 $(INSTALLED_SYSTEMIMAGE): $(BUILT_SYSTEMIMAGE) $(RECOVERY_FROM_BOOT_PATCH) | $(ACP)
 	@echo "Install system fs image: $@"