Simplify process exit-code handling on Posix, take 2.

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 e1b914b1a2f23e949f847cc3c0416e913119a025..0576c345df54453ffc17ec408c1672ddfc6407ed 100644
--- a/runtime/bin/platform_macos.cc
+++ b/runtime/bin/platform_macos.cc
@@ -27,15 +27,6 @@ bool Platform::Initialize() {
     perror("Setting signal handler failed");
     return false;
   }
-  // Unblock SIGCHLD as waiting on spawned child process depends
-  // on successful interception of this signal.
-  sigset_t newset;
-  sigemptyset(&newset);
-  sigaddset(&newset, SIGCHLD);
-  if (sigprocmask(SIG_UNBLOCK, &newset, NULL) != 0) {
-    perror("Unblocking SIGCHLD signal failed");
-  }
-
   return true;
 }