Improve benchmarking tool, add a few math benchmarks.

Change-Id: I641305dd0e4ac0705381e735ed1604c5be7aa536
diff --git a/tests/Android.mk b/tests/Android.mk
index ed1df6e..3217a4d 100644
--- a/tests/Android.mk
+++ b/tests/Android.mk
@@ -26,9 +26,11 @@
     -O2 \
     -Wall -Wextra \
     -Werror \
+    -fno-builtin \
 
 benchmark_src_files = \
     benchmark_main.cpp \
+    math_benchmark.cpp \
     string_benchmark.cpp \
 
 # Build benchmarks for the device (with bionic's .so). Run with: