Only copy libponyrt-pic.a on install if it exists (#3484)
Only copy libponyrt-pic.a on install if it exists (#3484)

On some platforms, it won't exist.
ponylang/ponyc,sgebbie/ponyc,dipinhora/ponyc,dipinhora/ponyc,sgebbie/ponyc,sgebbie/ponyc,ponylang/ponyc,dipinhora/ponyc,sgebbie/ponyc,ponylang/ponyc,jemc/ponyc,sgebbie/ponyc,jemc/ponyc,jemc/ponyc