system_error: provide a thread safe stringification for Windows

Provide a strerror_r replacement for Windows.  This is needed to build
libc++ for Windows with threading.

llvm-svn: 290851

libcxx/src/system_error.cpp

@@ -65,8 +65,16 @@ constexpr size_t strerror_buff_size = 1024;
 
 string do_strerror_r(int ev);
 
-#if defined(__linux__) && !defined(_LIBCPP_HAS_MUSL_LIBC)                      \
-    && (!defined(__ANDROID__) || __ANDROID_API__ >= 23)
+#if defined(_WIN32)
+string do_strerror_r(int ev) {
+  char buffer[strerror_buff_size];
+  if (::strerror_s(buffer, strerror_buff_size, ev) == 0)
+    return string(buffer);
+  std::snprintf(buffer, strerror_buff_size, "unknown error %d", ev);
+  return string(buffer);
+}
+#elif defined(__linux__) && !defined(_LIBCPP_HAS_MUSL_LIBC) &&                 \
+    (!defined(__ANDROID__) || __ANDROID_API__ >= 23)
 // GNU Extended version
 string do_strerror_r(int ev) {
     char buffer[strerror_buff_size];