Build: avoid compiling code for unused transports, routers, authenticators
The smtp transport is not covered here; there are dependencies in
other bits of the exim body.
- [DH] src/src/auths/cram_md5.c
- [DH] src/src/auths/dovecot.c
- [DH] src/src/auths/external.c
- [DH] src/src/auths/plaintext.c
- [DH] src/src/auths/spa.c
- [DH] src/src/auths/tls.c
- [DH] src/src/routers/accept.c
- [DH] src/src/routers/dnslookup.c
- [DH] src/src/routers/ipliteral.c
- [DH] src/src/routers/iplookup.c
- [DH] src/src/routers/manualroute.c
- [DH] src/src/routers/queryprogram.c
- [DH] src/src/routers/redirect.c
- [DH] src/src/transports/appendfile.c
- [DH] src/src/transports/autoreply.c
- [DH] src/src/transports/lmtp.c
- [DH] src/src/transports/pipe.c