Add the missing LOCAL_CFLAGS for librecovery.

The -DAB_OTA_UDPATER part was missing when separating the librecovery
module (commit 62e0bc7586077b3bde82759fb34b51b982cea20f).

Bug: 37300957
Test: Build sailfish recovery image and sideload full OTA.
Change-Id: Idd25662f6bc812c1aca95b096802f59b051f8d63
(cherry picked from commit 25dbe1717e3096ee59bfa4385cbcf80a972016a6)
diff --git a/Android.mk b/Android.mk
index 1b83d75..9e374de 100644
--- a/Android.mk
+++ b/Android.mk
@@ -47,6 +47,11 @@
     install.cpp
 LOCAL_CFLAGS := -Wno-unused-parameter -Werror
 LOCAL_CFLAGS += -DRECOVERY_API_VERSION=$(RECOVERY_API_VERSION)
+
+ifeq ($(AB_OTA_UPDATER),true)
+    LOCAL_CFLAGS += -DAB_OTA_UPDATER=1
+endif
+
 LOCAL_MODULE := librecovery
 LOCAL_STATIC_LIBRARIES := \
     libminui \