clarified comment about thread support on Tru64 Alpha and added osf to ifdef
clarified comment about thread support on Tru64 Alpha and added osf to ifdef

pyrovski/papi,pyrovski/papi,arm-hpc/papi,pyrovski/papi,arm-hpc/papi,pyrovski/papi,arm-hpc/papi,pyrovski/papi,pyrovski/papi,pyrovski/papi,arm-hpc/papi,pyrovski/papi,arm-hpc/papi,arm-hpc/papi,arm-hpc/papi