
Make sure we appropriately retry calls to read if the return result is less than what we asked for. Additionally, check and handle IO errors: EINTR results in the read operation getting restarted; other errors turn into exceptions. git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@210061 91177308-0d34-0410-b5e6-96231b3b80d8