Don't fail on EINTR, unless we have set a timeout.

[jlerouge]

Summary

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.

[tareqsiraj]

Looks ok.

[jlerouge]

Thanks, committed in r211918.

lib/Support/Unix/Program.inc

if (WaitUntilTerminates) {
     sigaction(SIGALRM, &Act, &Old);
     alarm(SecondsToWait);
   } else if (SecondsToWait == 0)
     WaitPidOptions = WNOHANG;
 
   // Parent process: Wait for the child process to terminate.
   int status;
   ProcessInfo WaitResult;
+
+  do {
     WaitResult.Pid = waitpid(ChildPid, &status, WaitPidOptions);
+  } while (WaitUntilTerminates && WaitResult.Pid == -1 && errno == EINTR);
+
   if (WaitResult.Pid != PI.Pid) {
     if (WaitResult.Pid == 0) {
       // Non-blocking wait.
       return WaitResult;
     } else {
       if (SecondsToWait && errno == EINTR) {
         // Kill the child.
         kill(PI.Pid, SIGKILL);