Also dump a stack trace on a pthread assertion failure

runtime/vm/os_thread_macos.cc

Index: runtime/vm/os_thread_macos.cc
diff --git a/runtime/vm/os_thread_macos.cc b/runtime/vm/os_thread_macos.cc
index 53034befa009463ef8116d99f45b02fe49a68136..92d04147d65a215a583f2e18c62ba554f5e98858 100644
--- a/runtime/vm/os_thread_macos.cc
+++ b/runtime/vm/os_thread_macos.cc
@@ -21,12 +21,15 @@
 #include "platform/assert.h"
 #include "platform/utils.h"
 
+#include "vm/profiler.h"
+
 namespace dart {
 
 #define VALIDATE_PTHREAD_RESULT(result)         \
   if (result != 0) { \
     const int kBufferSize = 1024; \
     char error_message[kBufferSize]; \
+    NOT_IN_PRODUCT(Profiler::DumpStackTrace(true /* native_stack_trace */)); \
     Utils::StrError(result, error_message, kBufferSize); \
     FATAL2("pthread error: %d (%s)", result, error_message); \
   }