Link iconv unconditionally

Author: Minoru

src/unix/mod.rs

@@ -293,6 +293,9 @@ pub const ATF_PERM: ::c_int = 0x04;
 pub const ATF_PUBL: ::c_int = 0x08;
 pub const ATF_USETRAILERS: ::c_int = 0x10;
 
+#[link(name = "iconv")]
+extern {}
+
 cfg_if! {
     if #[cfg(target_os = "l4re")] {
         // required libraries for L4Re are linked externally, ATM