Rename TARGET_OS_* to HOST_OS_*.

runtime/vm/cpuinfo_linux.cc

 // Copyright (c) 2012, 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_OS_LINUX)
+#if defined(HOST_OS_LINUX)
 
 #include "vm/cpuinfo.h"
 #include "vm/cpuid.h"
 #include "vm/proccpuinfo.h"
 
 #include "platform/assert.h"
 
 // As with Windows, on IA32 and X64, we use the cpuid instruction.
 // The analogous instruction is privileged on ARM and MIPS, so we resort to
 // reading from /proc/cpuinfo.
@@ skipping 82 matching lines @@
            (strcmp(field, fields_[kCpuInfoHardware]) == 0) ||
            (strcmp(field, fields_[kCpuInfoFeatures]) == 0);
   } else {
     ASSERT(method_ == kCpuInfoSystem);
     return ProcCpuInfo::HasField(field);
   }
 }
 
 }  // namespace dart
 
-#endif  // defined(TARGET_OS_LINUX)
+#endif  // defined(HOST_OS_LINUX)