Add O2 and DNDEBUG flags to libcapnp build
Add O2 and DNDEBUG flags to libcapnp build

jparyani/pycapnp,rcrowder/pycapnp,tempbottle/pycapnp,tempbottle/pycapnp,jparyani/pycapnp,jparyani/pycapnp,SymbiFlow/pycapnp,jparyani/pycapnp,rcrowder/pycapnp,rcrowder/pycapnp,tempbottle/pycapnp,SymbiFlow/pycapnp,rcrowder/pycapnp,SymbiFlow/pycapnp,tempbottle/pycapnp,SymbiFlow/pycapnp