Rename TARGET_OS_* to HOST_OS_*.

runtime/vm/signal_handler.h

 // 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.
 
 #ifndef RUNTIME_VM_SIGNAL_HANDLER_H_
 #define RUNTIME_VM_SIGNAL_HANDLER_H_
 
 #include "vm/allocation.h"
 #include "vm/globals.h"
 
-#if defined(TARGET_OS_LINUX)
+#if defined(HOST_OS_LINUX)
 #include <signal.h>    // NOLINT
 #include <ucontext.h>  // NOLINT
-#elif defined(TARGET_OS_ANDROID)
+#elif defined(HOST_OS_ANDROID)
 #include <signal.h>  // NOLINT
 #if !defined(__BIONIC_HAVE_UCONTEXT_T)
 #include <asm/sigcontext.h>  // NOLINT
 // If ucontext_t is not defined on Android, define it here.
 typedef struct sigcontext mcontext_t;
 typedef struct ucontext {
   uint32_t uc_flags;
   struct ucontext* uc_link;
   stack_t uc_stack;
   struct sigcontext uc_mcontext;
   uint32_t uc_sigmask;
 } ucontext_t;
 #endif                       // !defined(__BIONIC_HAVE_UCONTEXT_T)
-#elif defined(TARGET_OS_MACOS)
+#elif defined(HOST_OS_MACOS)
 #include <signal.h>        // NOLINT
 #include <sys/ucontext.h>  // NOLINT
-#elif defined(TARGET_OS_WINDOWS)
+#elif defined(HOST_OS_WINDOWS)
 // Stub out for windows.
 struct siginfo_t;
 struct mcontext_t;
 struct sigset_t {};
-#elif defined(TARGET_OS_FUCHSIA)
+#elif defined(HOST_OS_FUCHSIA)
 #include <signal.h>    // NOLINT
 #include <ucontext.h>  // NOLINT
 #endif
 
 
 // Old linux kernels on ARM might require a trampoline to
 // work around incorrect Thumb -> ARM transitions. See SignalHandlerTrampoline
 // below for more details.
 #if defined(HOST_ARCH_ARM) &&                                                  \
-    (defined(TARGET_OS_LINUX) || defined(TARGET_OS_ANDROID)) &&                \
+    (defined(HOST_OS_LINUX) || defined(HOST_OS_ANDROID)) &&                    \
     !defined(__thumb__)
 #define USE_SIGNAL_HANDLER_TRAMPOLINE
 #endif
 
 
 namespace dart {
 
 typedef void (*SignalAction)(int signal, siginfo_t* info, void* context);
 
 class SignalHandler : public AllStatic {
@@ skipping 56 matching lines @@
 #endif  // defined(USE_SIGNAL_HANDLER_TRAMPOLINE)
 };
 
 
 #undef USE_SIGNAL_HANDLER_TRAMPOLINE
 
 
 }  // namespace dart
 
 #endif  // RUNTIME_VM_SIGNAL_HANDLER_H_