Don't build libcxx_abi for unbundled projects.

It is preinstalled from prebuilts/sdk instead.

Change-Id: Ife0cec3a944fb3c4f7d77b4397decae58ff14529
diff --git a/Android.mk b/Android.mk
index 15e3d11..2c86fb3 100644
--- a/Android.mk
+++ b/Android.mk
@@ -14,6 +14,9 @@
 # limitations under the License.
 #
 
+# Don't build for unbundled branches
+ifeq (,$(TARGET_BUILD_APPS))
+
 # libcxxabi isn't working on mips yet
 ifneq ($(TARGET_ARCH),$(filter $(TARGET_ARCH), mips mips64))
 LOCAL_PATH := $(call my-dir)
@@ -96,3 +99,5 @@
 LOCAL_RTTI_FLAG := $(LIBCXXABI_RTTI_FLAG)
 include $(BUILD_HOST_SHARED_LIBRARY)
 endif
+
+endif  # TARGET_BUILD_APPS