lineage: More checks for copying AB backuptool scripts

Pixels tree have moved AB_OTA_PARTITIONS to BoardConfig.mk,
which is unavailable when parsing config/common.mk
In order to still copy AB backuptool scripts for them, check for
AB_OTA_POSTINSTALL_CONFIG too which still lives in device.mk

Change-Id: I871e2595bc4f083db6491de0d9574bae2794e654

config/common.mk

@@ -27,7 +27,7 @@ PRODUCT_COPY_FILES += \
     vendor/lineage/prebuilt/common/bin/backuptool.functions:install/bin/backuptool.functions \
     vendor/lineage/prebuilt/common/bin/50-lineage.sh:$(TARGET_COPY_OUT_SYSTEM)/addon.d/50-lineage.sh
 
-ifneq ($(AB_OTA_PARTITIONS),)
+ifneq ($(strip $(AB_OTA_PARTITIONS) $(AB_OTA_POSTINSTALL_CONFIG)),)
 PRODUCT_COPY_FILES += \
     vendor/lineage/prebuilt/common/bin/backuptool_ab.sh:$(TARGET_COPY_OUT_SYSTEM)/bin/backuptool_ab.sh \
     vendor/lineage/prebuilt/common/bin/backuptool_ab.functions:$(TARGET_COPY_OUT_SYSTEM)/bin/backuptool_ab.functions \