Fix arm64 build.

runtime/vm/cpu_arm64.cc

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/globals.h"
 
 #if defined(TARGET_ARCH_ARM64)
 
 #include "vm/cpu.h"
 #include "vm/cpuinfo.h"
 #include "vm/simulator.h"
 
 #if !defined(USING_SIMULATOR)
 #include <sys/syscall.h>  /* NOLINT */
 #include <unistd.h>  /* NOLINT */
 #endif
 
+#if defined(__linux__) || defined(ANDROID)
+extern "C" {
+void __clear_cache(char*, char*);
+}
+#endif
+
 namespace dart {
 
 void CPU::FlushICache(uword start, uword size) {
 #if TARGET_OS_IOS
   // Precompilation never patches code so there should be no I cache flushes.
   UNREACHABLE();
 #endif
 
 #if !defined(USING_SIMULATOR) && !TARGET_OS_IOS
   // Nothing to do. Flushing no instructions.
   if (size == 0) {
     return;
   }
 
   // ARM recommends using the gcc intrinsic __clear_cache on Linux and Android.
   // blogs.arm.com/software-enablement/141-caches-and-self-modifying-code/
   #if defined(__linux__) || defined(ANDROID)
-    extern void __clear_cache(char*, char*);
     char* beg = reinterpret_cast<char*>(start);
     char* end = reinterpret_cast<char*>(start + size);
-    ::__clear_cache(beg, end);
+    __clear_cache(beg, end);
   #else
     #error FlushICache only tested/supported on Linux and Android
   #endif
 
 #endif
 }
 
 
 const char* CPU::Id() {
   return
@@ skipping 50 matching lines @@
   ASSERT(hardware_ != NULL);
   free(const_cast<char*>(hardware_));
   hardware_ = NULL;
   CpuInfo::Cleanup();
 }
 #endif  // !defined(USING_SIMULATOR)
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_ARM64