openssl: set openssl_platform for ARM Linux
openssl: set openssl_platform for ARM Linux

https://bugzilla.gnome.org/show_bug.cgi?id=794824

nirbheek/cerbero,centricular/cerbero,fluendo/cerbero,GStreamer/cerbero,GStreamer/cerbero,fluendo/cerbero,atsushieno/cerbero,GStreamer/cerbero,nirbheek/cerbero,centricular/cerbero,GStreamer/cerbero,fluendo/cerbero,centricular/cerbero,centricular/cerbero,atsushieno/cerbero,fluendo/cerbero,centricular/cerbero,nirbheek/cerbero,atsushieno/cerbero,atsushieno/cerbero,GStreamer/cerbero,atsushieno/cerbero,fluendo/cerbero,nirbheek/cerbero