Revert r43217, r43215, r43208, r43207, and r43202.

runtime/bin/process_macos.cc

Index: runtime/bin/process_macos.cc
diff --git a/runtime/bin/process_macos.cc b/runtime/bin/process_macos.cc
index 3df775f568c933aa4a0d99a9d5a610083fdac2be..a6d9301b421cd5f83e0224e7135908aa873f9d50 100644
--- a/runtime/bin/process_macos.cc
+++ b/runtime/bin/process_macos.cc
@@ -7,7 +7,6 @@
 
 #include "bin/process.h"
 
-#include <crt_externs.h>  // NOLINT
 #include <errno.h>  // NOLINT
 #include <fcntl.h>  // NOLINT
 #include <poll.h>  // NOLINT
@@ -25,6 +24,8 @@
 #include "platform/signal_blocker.h"
 
 
+extern char **environ;
+
 
 namespace dart {
 namespace bin {
@@ -473,9 +474,6 @@ int Process::Start(const char* path,
       }
 
       if (program_environment != NULL) {
-        // On MacOS you have to do a bit of magic to get to the
-        // environment strings.
-        char** environ = *(_NSGetEnviron());
         environ = program_environment;
       }