Direct OS:Print[Err] to syslog on iOS.

runtime/vm/os_macos.cc

Index: runtime/vm/os_macos.cc
diff --git a/runtime/vm/os_macos.cc b/runtime/vm/os_macos.cc
index 362ad0165764684b56b3b708d2a4dac9c60679ed..a7d3ee672364ef5fedf66fbb956ddf1a5bd1e546 100644
--- a/runtime/vm/os_macos.cc
+++ b/runtime/vm/os_macos.cc
@@ -16,7 +16,8 @@
 #include <sys/resource.h>  // NOLINT
 #include <unistd.h>  // NOLINT
 #if TARGET_OS_IOS
-#include <sys/sysctl.h>
+#include <sys/sysctl.h>  // NOLINT
+#include <syslog.h>  // NOLINT
 #endif
 
 #include "platform/utils.h"
@@ -143,7 +144,7 @@ void OS::AlignedFree(void* ptr) {
 intptr_t OS::ActivationFrameAlignment() {
 #if TARGET_OS_IOS
 #if TARGET_ARCH_ARM
-  // Even if we generate code that maintains a strong alignment, we cannot
+  // Even if we generate code that maintains a stronger alignment, we cannot
   // assert the stronger stack alignment because C++ code will not maintain it.
   return 8;
 #elif TARGET_ARCH_ARM64
@@ -234,10 +235,17 @@ char* OS::StrNDup(const char* s, intptr_t n) {
 
 
 void OS::Print(const char* format, ...) {
+#if TARGET_OS_IOS
+  va_list args;
+  va_start(args, format);
+  vsyslog(LOG_INFO, format, args);
+  va_end(args);
+#else
   va_list args;
   va_start(args, format);
   VFPrint(stdout, format, args);
   va_end(args);
+#endif
 }
 
 
@@ -322,10 +330,17 @@ void OS::RegisterCodeObservers() {
 
 
 void OS::PrintErr(const char* format, ...) {
+#if TARGET_OS_IOS
+  va_list args;
+  va_start(args, format);
+  vsyslog(LOG_ERR, format, args);
+  va_end(args);
+#else
   va_list args;
   va_start(args, format);
   VFPrint(stderr, format, args);
   va_end(args);
+#endif
 }