Add FreeBSD compilation support

Update these scripts (and add specific FreeBSD automate.py file) in order to get DocumentServer compiling under FreeBSD. Please note that :

I added the ability to put patch files into "patches//" directory which will be applied on the fetched git repositories before compilation. If this directory does not exist it does nothing. This can be a good solution in order to test compilation on patched git repositories ; "core_and_multimedia" has been disabled for FreeBSD since Chromium compilation needs a custom compilation process under FreeBSD ; I restricted compilation to "server" only since I didn't worked on compilation of the other modules. Last but not least, CC and CXX environment variables must be set respectively to clang and clang++ before executing automate.py since the pkg node's binary needs it. I tried to use base.set_env before calling pkg but for some reasons these environment variables are not passed to pkg.

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