Add clang-toolchain cmake file to allow building with clang on gcc platforms
Add clang-toolchain cmake file to allow building with clang on gcc platforms

htcondor/htcondor,htcondor/htcondor,htcondor/htcondor,htcondor/htcondor,htcondor/htcondor,htcondor/htcondor,htcondor/htcondor,htcondor/htcondor