Makefile: only build runc for static target
Makefile: only build runc for static target

There is no need to have a static version of recvtty and/or sd-helper
binary.

This speeds up script/release.sh a bit.

Signed-off-by: Kir Kolyshkin <3a017b8ddb3f9cf3e4a59978b004111bdeb97f08@gmail.com>

opencontainers/runc,opencontainers/runc,rhatdan/runc,opencontainers/runc,kolyshkin/runc,kolyshkin/runc,rhatdan/runc,kolyshkin/runc,rhatdan/runc,rhatdan/runc,kolyshkin/runc,opencontainers/runc