Fix redirection of stderr in sys::Program::ExecuteAndWait. There was logic

Fix redirection of stderr in sys::Program::ExecuteAndWait. There was logic
error that caused it to redirect stderr to stdout too often.

This fix is applied identically to the win32 code as well, but that is
untested.
--Thi line, and those below, will be ignored--

M    System/Unix/Program.inc
M    System/Win32/Program.inc

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@52233 91177308-0d34-0410-b5e6-96231b3b80d8