Record and link with used native libraries.

src/lib/linux_os.rs

@@ -5,7 +5,7 @@ import vec::vbuf;
 
 // FIXME Somehow merge stuff duplicated here and macosx_os.rs. Made difficult
 // by https://github.com/graydon/rust/issues#issue/268
-native "cdecl" mod libc {
+native "cdecl" mod libc = "c" {
     fn open(sbuf s, int flags, uint mode) -> int;
     fn read(int fd, vbuf buf, uint count) -> int;
     fn write(int fd, vbuf buf, uint count) -> int;