Add stubs in platform_macos and file_system_watcher_macos for building the same

runtime/bin/platform_macos.cc

Index: runtime/bin/platform_macos.cc
diff --git a/runtime/bin/platform_macos.cc b/runtime/bin/platform_macos.cc
index 351a829db717d47f0f0159d62b39fc06ddba3635..6e006c08a7c3f760488f9b9650d2dfc19bc2acf1 100644
--- a/runtime/bin/platform_macos.cc
+++ b/runtime/bin/platform_macos.cc
@@ -3,14 +3,16 @@
 // BSD-style license that can be found in the LICENSE file.
 
 #include "platform/globals.h"
-#if defined(TARGET_OS_MACOS)
+#if defined(TARGET_OS_MACOS) || defined(TARGET_OS_IOS)

[Ivan Posva, 2015/06/09 21:20:03]

Please note that TARGET_OS_IOS also automatically means that TARGET_OS_MACOS is
defined. I am fine either way here, even if it is a bit redundant.

 
 #include <mach-o/dyld.h>
 
 #include "bin/file.h"
 #include "bin/platform.h"
 
+#if !defined(TARGET_OS_IOS)
 #include <crt_externs.h>  // NOLINT
+#endif
 #include <signal.h>  // NOLINT
 #include <string.h>  // NOLINT
 #include <unistd.h>  // NOLINT
@@ -57,6 +59,9 @@ bool Platform::LocalHostname(char *buffer, intptr_t buffer_length) {
 
 
 char** Platform::Environment(intptr_t* count) {
+#if defined(TARGET_OS_IOS)
+  return NULL;

[Ivan Posva, 2015/06/09 21:20:03]

Is there really no way to access environment variables on iOS?

+#else
   // 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
@@ -71,6 +76,7 @@ char** Platform::Environment(intptr_t* count) {
     result[current] = environ[current];
   }
   return result;
+#endif
 }