fix signed/unsigned comparison issue (on OpenBSD)
fix signed/unsigned comparison issue (on OpenBSD)

empiredan/googletest,google/googletest,empiredan/googletest,google/googletest,gianricardo/googletest,antidotcb/googletest,antidotcb/googletest,google/googletest,antidotcb/googletest,gianricardo/googletest,google/googletest,empiredan/googletest,antidotcb/googletest,gianricardo/googletest