Rename TARGET_OS_* to HOST_OS_*.

runtime/vm/malloc_hooks.cc

 // Copyright (c) 2017, 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 "platform/globals.h"
 
 #if defined(DART_USE_TCMALLOC) && !defined(PRODUCT) &&                         \
-    !defined(TARGET_ARCH_DBC) && !defined(TARGET_OS_FUCHSIA)
+    !defined(TARGET_ARCH_DBC) && !defined(HOST_OS_FUCHSIA)
 
 #include "vm/malloc_hooks.h"
 
 #include "gperftools/malloc_hook.h"
 
 #include "platform/assert.h"
 #include "vm/hash_map.h"
 #include "vm/json_stream.h"
 #include "vm/os_thread.h"
 #include "vm/profiler.h"
@@ skipping 418 matching lines @@
           allocation_info->allocation_size());
       MallocHooksState::address_map()->Remove(ptr);
       delete allocation_info;
     }
   }
 }
 
 }  // namespace dart
 
 #endif  // defined(DART_USE_TCMALLOC) && !defined(PRODUCT) &&
-        // !defined(TARGET_ARCH_DBC) && !defined(TARGET_OS_FUCHSIA)
+        // !defined(TARGET_ARCH_DBC) && !defined(HOST_OS_FUCHSIA)