Add a test for SafeMath.

Change-Id: I445cd168e6f22a4c12f954eb94e32bd28dba9501
diff --git a/build/Android.gtest.mk b/build/Android.gtest.mk
index 63200b7..00fbd69 100644
--- a/build/Android.gtest.mk
+++ b/build/Android.gtest.mk
@@ -111,6 +111,7 @@
   runtime/indirect_reference_table_test.cc \
   runtime/instruction_set_test.cc \
   runtime/intern_table_test.cc \
+  runtime/interpreter/safe_math_test.cc \
   runtime/leb128_test.cc \
   runtime/mem_map_test.cc \
   runtime/mirror/dex_cache_test.cc \