lldb can interrupt waitpid, so EINTR shouldn't be an error. This fixes the case

lldb can interrupt waitpid, so EINTR shouldn't be an error. This fixes the case
where there is no timeout. In the case where there is a timeout though, the
code is still wrong since it doesn't check that the alarm really went off.

Without this patch, I cannot debug a program that forks itself using
sys::ExecuteAndWait with lldb.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@211918 91177308-0d34-0410-b5e6-96231b3b80d8