FileIOResult is not a std::expected or similar. Don't treat it that way.

Author: Sterling-Augustine

libc/src/stdio/printf_core/vfprintf_internal.h

@@ -55,10 +55,7 @@ LIBC_INLINE FileIOResult fwrite_unlocked(const void *ptr, size_t size,
   // if there was an error, and errno may have previously been nonzero. Only
   // return errno if there was an error.
   auto bytes = ::fwrite_unlocked(ptr, size, nmemb, f);
-  if (bytes == nmemb * size)
-    return bytes;
-  else
-    return errno;
+  return {bytes, bytes == nmemb * size ? 0 : errno};
 }
 #endif // LIBC_COPT_STDIO_USE_SYSTEM_FILE
 } // namespace internal