Use signal-block around fork() to avoid we block it.

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 185ca0bab5abd52bea5305d77cd6b7f7cec3f5c8..5c85d9a3047e73055ea47dcd08b79fa197b20e58 100644
--- a/runtime/bin/process_macos.cc
+++ b/runtime/bin/process_macos.cc
@@ -150,7 +150,7 @@ class ExitCodeHandler {
     running_ = false;
 
     // Fork to wake up waitpid.
-    if (TEMP_FAILURE_RETRY(fork()) == 0) {
+    if (TEMP_FAILURE_RETRY_BLOCK_SIGNALS(fork()) == 0) {
       exit(0);
     }
 
@@ -349,7 +349,7 @@ int Process::Start(const char* path,
     program_environment[environment_length] = NULL;
   }
 
-  pid = TEMP_FAILURE_RETRY(fork());
+  pid = TEMP_FAILURE_RETRY_BLOCK_SIGNALS(fork());
   if (pid < 0) {
     SetChildOsErrorMessage(os_error_message);
     delete[] program_arguments;