Add _android files for building DartVM on Android

runtime/bin/platform_android.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 "bin/platform.h"
 
-#include <crt_externs.h>
 #include <signal.h>
 #include <string.h>
 #include <unistd.h>
 
 
 bool Platform::Initialize() {
   // Turn off the signal handler for SIGPIPE as it causes the process
   // to terminate on writing to a closed pipe. Without the signal
   // handler error EPIPE is set instead.
   struct sigaction act;
   bzero(&act, sizeof(act));
   act.sa_handler = SIG_IGN;
   if (sigaction(SIGPIPE, &act, 0) != 0) {
     perror("Setting signal handler failed");
     return false;
   }
   return true;
 }
 
 
 int Platform::NumberOfProcessors() {
   return sysconf(_SC_NPROCESSORS_ONLN);
 }
 
 
 const char* Platform::OperatingSystem() {
-  return "macos";
+  return "android";
 }
 
 
 bool Platform::LocalHostname(char *buffer, intptr_t buffer_length) {
   return gethostname(buffer, buffer_length) == 0;
 }
 
 
 char** Platform::Environment(intptr_t* count) {
   // Using environ directly is only safe as long as we do not
   // provide access to modifying environment variables.
-  // On MacOS you have to do a bit of magic to get to the
-  // environment strings.
-  char** environ = *(_NSGetEnviron());
   intptr_t i = 0;
   char** tmp = environ;
   while (*(tmp++) != NULL) i++;
   *count = i;
   char** result = new char*[i];
   for (intptr_t current = 0; current < i; current++) {
     result[current] = environ[current];
   }
   return result;
 }
 
 
 char* Platform::StrError(int error_code) {
   static const int kBufferSize = 1024;
   char* error = static_cast<char*>(malloc(kBufferSize));
   error[0] = '\0';
   strerror_r(error_code, error, kBufferSize);
   return error;
 }