Do not force symbols to be defined in library dependencies.

E.g. libc has undefined references to symbols in libdl. Other linking
errors were also observed in practice; it is currently somewhat unclear
whether those are legitimate or not. Further investigation to follow.

Change-Id: I1fac07a506639a47660ae5a1b2ef36e1dc64fa9b
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>