Fix mips64 build

Added missing include.

Test: successful aosp_mips64-eng build
Change-Id: I88ee9d9c6f8b159da4a1a4bb92c194d6355868ee
diff --git a/runtime/arch/mips64/entrypoints_init_mips64.cc b/runtime/arch/mips64/entrypoints_init_mips64.cc
index 763d93e..007f7b3 100644
--- a/runtime/arch/mips64/entrypoints_init_mips64.cc
+++ b/runtime/arch/mips64/entrypoints_init_mips64.cc
@@ -14,6 +14,7 @@
  * limitations under the License.
  */
 
+#include <math.h>
 #include <string.h>
 
 #include "atomic.h"