Replaced strerror() calls with threadsafe strerror_r()

runtime/platform/thread_macos.cc

Index: runtime/platform/thread_macos.cc
diff --git a/runtime/platform/thread_macos.cc b/runtime/platform/thread_macos.cc
index 29059fe4ca910270230be83b824de669f97dd43d..e9c6dfc38e85987b61ce4a52414bbafc26e88bda 100644
--- a/runtime/platform/thread_macos.cc
+++ b/runtime/platform/thread_macos.cc
@@ -15,15 +15,21 @@ namespace dart {
 
 #define VALIDATE_PTHREAD_RESULT(result)         \
   if (result != 0) { \
-    FATAL2("pthread error: %d (%s)", result, strerror(result)); \
+    const int kBufferSize = 1024; \
+    char error_message[kBufferSize]; \
+    strerror_r(result, error_message, kBufferSize); \
+    FATAL2("pthread error: %d (%s)", result, error_message); \
   }
 
 
 #ifdef DEBUG
 #define RETURN_ON_PTHREAD_FAILURE(result) \
   if (result != 0) { \
+    const int kBufferSize = 1024; \
+    char error_message[kBufferSize]; \
+    strerror_r(result, error_message, kBufferSize); \
     fprintf(stderr, "%s:%d: pthread error: %d (%s)\n", \
-            __FILE__, __LINE__, result, strerror(result)); \
+            __FILE__, __LINE__, result, error_message); \
     return result; \
   }
 #else