[build] Fix header-hygiene warnings for arm64

This prepares for switching arm64 sim to gn.

BUG=chromium:474921

Review-Url: https://codereview.chromium.org/2174363002
Cr-Commit-Position: refs/heads/master@{#38033}

test/cctest/test-utils-arm64.cc

@@ -32,7 +32,8 @@
 #include "test/cctest/cctest.h"
 #include "test/cctest/test-utils-arm64.h"
 
-using namespace v8::internal;
+namespace v8 {
+namespace internal {
 
 
 #define __ masm->
@@ -423,3 +424,6 @@ void RegisterDump::Dump(MacroAssembler* masm) {
 
   completed_ = true;
 }
+
+}  // namespace internal
+}  // namespace v8

test/cctest/test-utils-arm64.h

@@ -36,7 +36,8 @@
 #include "src/macro-assembler.h"
 
 
-using namespace v8::internal;
+namespace v8 {
+namespace internal {
 
 
 // RegisterDump: Object allowing integer, floating point and flags registers
@@ -230,4 +231,7 @@ void ClobberFP(MacroAssembler* masm, RegList reg_list,
 // Clobber or ClobberFP functions.
 void Clobber(MacroAssembler* masm, CPURegList reg_list);
 
+}  // namespace internal
+}  // namespace v8
+
 #endif  // V8_ARM64_TEST_UTILS_ARM64_H_