U.S. stocks were poised to open flat on Friday, ahead of data on the housing market, with the S&P 500 on track to notch its first weekly gain in the past three. Expectations call for sales of single-family homes to climb to 425,000 units from the seasonally adjusted annual rate of 384,000 units in the prior month. The S&P 500 ended higher for a second session on Thursday, as gains in small-cap stocks help buoy investor confidence, while the Nasdaq climbed on a rally in biotech shares.