Report lli remote IO errors consistently

This enables IO error reports in both the child and server processes.

The scheme still isn't entirely satisfactory and output is jumbled but it beats
having no output at all. This will hopefully unblock ARM support (PR18057).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@200017 91177308-0d34-0410-b5e6-96231b3b80d8