build: don't depend on the LINK_LIBRARIES target property for plugins
build: don't depend on the LINK_LIBRARIES target property for plugins

Without this using system libraries instead of the bundled code will
fail on older CMake versions (such as 2.8.7, which is used on Ubuntu
12.04).

Cloudef/squash,quixdb/squash,Cloudef/squash,Cloudef/squash,jibsen/squash,jibsen/squash,quixdb/squash,jibsen/squash,quixdb/squash