Move RoS allocator to use unordered_set.

Work-around existing stlport issues for the target. This will go away when the
target is using libc++.

Change-Id: I8f213ecd9dc7d93d17f4a0d7e84182c12af6ca1b
diff --git a/build/Android.common.mk b/build/Android.common.mk
index 188ddb5..74f8d8d 100644
--- a/build/Android.common.mk
+++ b/build/Android.common.mk
@@ -253,6 +253,9 @@
 endif
 ART_TARGET_CFLAGS += $(ART_DEFAULT_GC_TYPE_CFLAGS)
 
+# TODO: remove when target no longer implies stlport.
+ART_TARGET_CFLAGS += -DART_WITH_STLPORT=1
+
 # DEX2OAT_TARGET_INSTRUCTION_SET_FEATURES is set in ../build/core/dex_preopt.mk based on
 # the TARGET_CPU_VARIANT
 ifeq ($(DEX2OAT_TARGET_INSTRUCTION_SET_FEATURES),)