- Add OS::StrNDup instead of redefining it when needed.

runtime/vm/os_macos.cc

Index: runtime/vm/os_macos.cc
===================================================================
--- runtime/vm/os_macos.cc	(revision 21320)
+++ runtime/vm/os_macos.cc	(working copy)
@@ -135,6 +135,30 @@
 }
 
 
+char* OS::StrNDup(const char* s, intptr_t n) {
+  // strndup has only been added to Mac OS X in 10.7. We are supplying
+  // our own copy here if needed.
+#if !defined(__ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__) || \
+    __ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__ <= 1060
+  intptr_t len = strlen(s);
+  if ((n < 0) || (len < 0)) {
+    return NULL;
+  }
+  if (n < len) {
+    len = n;
+  }
+  char* result = reinterpret_cast<char*>(malloc(len + 1));
+  if (result == NULL) {
+    return NULL;
+  }
+  result[len] = '\0';
+  return reinterpret_cast<char*>(memcpy(result, s, len));
+#else  // !defined(__ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__) || ...
+  return strndup(s, n);
+#endif  // !defined(__ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__) || ...
+}
+
+
 void OS::Print(const char* format, ...) {
   va_list args;
   va_start(args, format);