Otherwise that #ifdef in visibility.h is useless, and __declspec(dllimport)
will be always on.
Fixes: #314
Fixes: 4545fa9b6866df47ce2f908631a84477a94d5f49 ("Add option to build shared
library")
We had cmake and autoconf tests for the inet_aton function... but we
never actually use it any more.
(The autoconf tests still use the callability of inet_aton to decide
whether we need to link against -lresolv)
Reported by Harlan Stenn.