net: fix res_search uses on alpine, android, dragonfly
On Android and Dragonfly, don't use -lresolv. It doesn't exist there.
On Linux, use res_search instead of res_nsearch.
glibc makes res_search thread-safe by having a per-thread __res.
It still also provides res_nsearch.
musl makes res_search thread-safe by ignoring __res completely.
It does not provide res_nsearch at all.
Changing to res_search on Linux will fix builds on musl-based systems
while keeping glibc-based systems working.