Enable the use of [SU]Int32Size and EnumSize templates for AArch64

When benchmarking proto_benchmark from fleetbench on an AArch64 target we found
that clang is able to vectorize these functions and they offer better
performance than the scalar alternative.

src/google/protobuf/wire_format_lite.cc

@@ -704,7 +704,7 @@ static size_t VarintSize64(const T* data, const int n) {
 // and other platforms are untested, in those cases using the optimized
 // varint size routine for each element is faster.
 // Hence we enable it only for clang
-#if defined(__SSE__) && defined(__clang__)
+#if (defined(__SSE__) || defined(__aarch64__)) && defined(__clang__)
 size_t WireFormatLite::Int32Size(const RepeatedField<int32_t>& value) {
   return VarintSize<false, true>(value.data(), value.size());
 }
@@ -722,7 +722,7 @@ size_t WireFormatLite::EnumSize(const RepeatedField<int>& value) {
   return VarintSize<false, true>(value.data(), value.size());
 }
 
-#else  // !(defined(__SSE4_1__) && defined(__clang__))
+#else  // !((defined(__SSE4_1__) || defined(__aarch64__) && defined(__clang__))
 
 size_t WireFormatLite::Int32Size(const RepeatedField<int32_t>& value) {
   size_t out = 0;