Enable SurfaceTexture fence sync for the emulator

The host-accelerated GL ES driver doesn't do the implicit
synchronization required when fence sync isn't used.

Bug: 6515813
Change-Id: I6a667f2db6b519f3557b5abda78775f767841dae
diff --git a/libs/gui/Android.mk b/libs/gui/Android.mk
index 8bda3aa..8224847 100644
--- a/libs/gui/Android.mk
+++ b/libs/gui/Android.mk
@@ -42,6 +42,10 @@
 ifeq ($(TARGET_BOARD_PLATFORM), s5pc110)
 	LOCAL_CFLAGS += -DUSE_FENCE_SYNC
 endif
+ifneq ($(filter generic%,$(TARGET_DEVICE)),)
+    # Emulator build
+    LOCAL_CFLAGS += -DUSE_FENCE_SYNC
+endif
 
 ifeq ($(TARGET_BOARD_PLATFORM), tegra)
 	LOCAL_CFLAGS += -DALLOW_DEQUEUE_CURRENT_BUFFER