/usr/bin/js78 installed by spidermonkey has pie enabled on its own: checksec --file=/usr/bin/js78 RELRO STACK CANARY NX PIE RPATH RUNPATH Symbols FORTIFY Fortified Fortifiable FILE Partial_RELRO No canary found NX enabled PIE_enabled No RPATH No RUNPATH No Symbols Yes 10 26 /usr/bin/js78 checksec utility comes from app-admin/checksec
I don't think we are going to expose "--enable-pie". EXTRA_CONF is your friend.