Log Message:
Update to last stable release under the polarssl brand. The list of changes
is very long and, if you're interested, they can be found here:

https://tls.mbed.org/download-archive

by reading all the ChangeLogs from 1.2.12-1.3.9. The pkgsrc changes are:

Use cmake for build, as that's what upstream recommends and is less likely
to fail cross-platform for future releases. Needs pkg-config due to that.
Build and install shared library. Remove executable permission from static
library during post-install. Needs pthreads and openssl. Tested this build
against the build of latest version of powerdns (update coming).