Add missing safe_math_arm_impl header

Change-Id: I25826d97615d540b04494b46e8abc4a209146ae3

base/BUILD

diff --git a/base/BUILD b/base/BUILD
index c922b73..32c3b9c 100644
--- a/base/BUILD
+++ b/base/BUILD
@@ -42,6 +42,7 @@
         "numerics/safe_conversions.h",
         "numerics/safe_conversions_arm_impl.h",
         "numerics/safe_conversions_impl.h",
+        "numerics/safe_math_arm_impl.h",
         "numerics/safe_math_clang_gcc_impl.h",
         "numerics/safe_math_shared_impl.h",
         "ranges/algorithm.h",