Make it possible to enable heap poisoning via make variable.

If ART_HEAP_POISONING=true, build with heap poisoning enabled.

Bug: 8367515
Change-Id: I818e86047e6dd99b5bc9920713ef943a65b677e6
diff --git a/build/Android.common_build.mk b/build/Android.common_build.mk
index 6346970..7620e76 100644
--- a/build/Android.common_build.mk
+++ b/build/Android.common_build.mk
@@ -237,6 +237,10 @@
   art_cflags += -DART_USE_OPTIMIZING_COMPILER=1
 endif
 
+ifeq ($(ART_HEAP_POISONING),true)
+  art_cflags += -DART_HEAP_POISONING=1
+endif
+
 # Cflags for non-debug ART and ART tools.
 art_non_debug_cflags := \
   -O3