Make sure output directories exist in case we're building outside the source dir.
Make sure output directories exist in case we're building outside the source dir.

persmule/libsrtp,Distrotech/libsrtp,Distrotech/libsrtp,cuijinquan/libsrtp,persmule/libsrtp,yarrcc/libsrtp-ios,cuijinquan/libsrtp,cuijinquan/libsrtp,persmule/libsrtp,yarrcc/libsrtp-ios,ksophocleous/libsrtp,yarrcc/libsrtp-ios,ksophocleous/libsrtp