Move signal_blocker to platform and use it by default in TEMP_FAILURE_RETRY.

runtime/bin/crypto_macos.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 "platform/globals.h"
 #if defined(TARGET_OS_MACOS)
 
 #include <errno.h>  // NOLINT
 #include <fcntl.h>  // NOLINT
 
 #include "bin/fdutils.h"
 #include "bin/crypto.h"
 
+#include "platform/signal_blocker.h"
+
 
 namespace dart {
 namespace bin {
 
 bool Crypto::GetRandomBytes(intptr_t count, uint8_t* buffer) {
   intptr_t fd = TEMP_FAILURE_RETRY(open("/dev/urandom", O_RDONLY));
   if (fd < 0) return false;
   intptr_t bytes_read = read(fd, buffer, count);
   close(fd);
   return bytes_read == count;
 }
 
 }  // namespace bin
 }  // namespace dart
 
 #endif  // defined(TARGET_OS_MACOS)