Add a boolean parameter to the ExecuteAndWait static function to indicated
if execution failed.  ExecuteAndWait returns -1 upon an execution failure, but
checking the return value isn't sufficient because the wait command may
return -1 as well.  This new parameter is to be used by the clang driver in a
subsequent commit.
Part of rdar://13362359


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@178087 91177308-0d34-0410-b5e6-96231b3b80d8