res_init is __res_init; doesn't need -lresolv

glibc 2.2 deprecated res_init, and renamed it as __res_init:
https://bugzilla.redhat.com/show_bug.cgi?id=43822#c6
res_init keeps working in C for programs that directly use resolv.h,
since it redefines the symbol in a macro, but this won't work in Rust
land.

Author: jonhoo

src/unix/mod.rs

@@ -229,7 +229,6 @@ cfg_if! {
                         target_os = "bitrig"))] {
         #[link(name = "c")]
         #[link(name = "m")]
-        #[link(name = "resolv")]
         extern {}
     } else if #[cfg(target_os = "haiku")] {
         #[link(name = "root")]
@@ -243,7 +242,6 @@ cfg_if! {
         #[link(name = "c")]
         #[link(name = "m")]
         #[link(name = "rt")]
-        #[link(name = "resolv")]
         #[link(name = "pthread")]
         extern {}
     }
@@ -696,6 +694,7 @@ extern {
                        res: *mut *mut addrinfo) -> ::c_int;
     pub fn freeaddrinfo(res: *mut addrinfo);
     pub fn gai_strerror(errcode: ::c_int) -> *const ::c_char;
+    #[link_name = "__res_init"]
     pub fn res_init() -> ::c_int;
 
     #[cfg_attr(target_os = "netbsd", link_name = "__gmtime_r50")]