rtags: fix darwin build

Adds dependency to MacOS_SDK 10.9 and accordingly to the macosx
deployment target to configure SDK-based deployment in rtags. In detail,
rtags makes use of launch_activate_socket() which is available in
launchd.h >10.9. Latter is still not available through
apple-opensource-releases, if ever. Thus, the deployment target and
build input have to be added to let rtags build scripts make use of MAC_OS_X_VERSION_MAX_ALLOWED correctly.