[fuchsia, arm64] Use mx_cache_flush instead of removed __clear_cache.

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/cpu_arm64.h"
 
@@ skipping 16 matching lines @@
 #endif
 
 #if !defined(USING_SIMULATOR) && !HOST_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(HOST_OS_ANDROID) || defined(HOST_OS_FUCHSIA) ||                    \
-    defined(HOST_OS_LINUX)
+#if defined(HOST_OS_ANDROID) || defined(HOST_OS_LINUX)
   extern void __clear_cache(char*, char*);
   char* beg = reinterpret_cast<char*>(start);
   char* end = reinterpret_cast<char*>(start + size);
   ::__clear_cache(beg, end);
+#elif defined(HOST_OS_FUCHSIA)
+  // TODO(magenta): Use MX_CACHE_FLUSH_INSTR when implemented.
+  // mx_status result = mx_cache_flush(start, size, MX_CACHE_FLUSH_INSN);

[Roland McGrath, 2017/07/25 22:34:24]

This should build now and the Magenta runtime support will probably land within
a day, so I think you could just enable this now.

[rmacnak, 2017/07/25 22:38:15]

I can't call it now because the current implementation is a trap instead of
no-op.

+  // ASSERT(result == MX_OK);
 #else
 #error FlushICache only tested/supported on Android, Fuchsia, and Linux
 #endif
 
 #endif
 }
 
 const char* CPU::Id() {
   return
 #if defined(USING_SIMULATOR)
@@ skipping 45 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