prebuilt: Avoid re-linking ARM64 specific library on other architectures

libclang_rt.ubsan_standalone-aarch64-android.so is a library for
arm64 and is therefore not available on other architectures, causing
the build to fail because there is no rule to build it.

Change-Id: Ia4af38f42ba46a233d40e936d43e4c97c449d059
diff --git a/prebuilt/Android.mk b/prebuilt/Android.mk
index f792042..26ee594 100644
--- a/prebuilt/Android.mk
+++ b/prebuilt/Android.mk
@@ -346,7 +346,9 @@
     endif
 endif
 ifeq ($(shell test $(PLATFORM_SDK_VERSION) -gt 27; echo $$?),0)
-    RELINK_SOURCE_FILES += $(TARGET_OUT_SHARED_LIBRARIES)/libclang_rt.ubsan_standalone-aarch64-android.so
+    ifeq ($(TARGET_ARCH), arm64)
+        RELINK_SOURCE_FILES += $(TARGET_OUT_SHARED_LIBRARIES)/libclang_rt.ubsan_standalone-aarch64-android.so
+    endif
     RELINK_SOURCE_FILES += $(TARGET_OUT_SHARED_LIBRARIES)/liblogwrap.so
     RELINK_SOURCE_FILES += $(TARGET_OUT_SHARED_LIBRARIES)/libext2_misc.so
 endif