Rename TARGET_OS_* to HOST_OS_*.

runtime/vm/signal_handler_macos.cc

 // Copyright (c) 2013, 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"
 #include "vm/instructions.h"
 #include "vm/simulator.h"
 #include "vm/signal_handler.h"
-#if defined(TARGET_OS_MACOS)
+#if defined(HOST_OS_MACOS)
 
 namespace dart {
 
 uintptr_t SignalHandler::GetProgramCounter(const mcontext_t& mcontext) {
   uintptr_t pc = 0;
 
 #if defined(HOST_ARCH_IA32)
   pc = static_cast<uintptr_t>(mcontext->__ss.__eip);
 #elif defined(HOST_ARCH_X64)
   pc = static_cast<uintptr_t>(mcontext->__ss.__rip);
@@ skipping 93 matching lines @@
   act.sa_handler = SIG_IGN;
   sigemptyset(&act.sa_mask);
   act.sa_flags = 0;
   int r = sigaction(SIGPROF, &act, NULL);
   ASSERT(r == 0);
 }
 
 
 }  // namespace dart
 
-#endif  // defined(TARGET_OS_MACOS)
+#endif  // defined(HOST_OS_MACOS)