Repace use of static_nobundle with native_link_modifiers

This fixes warning when building Rust and running tests:
```
warning: library kind `static-nobundle` has been superseded by specifying `-bundle` on library kind `static`. Try `static:-bundle`
warning: `rustc_llvm` (lib) generated 2 warnings (1 duplicate)
```

Author: mati865

unwind/src/lib.rs

@@ -5,7 +5,6 @@
 #![feature(native_link_modifiers_bundle)]
 #![feature(nll)]
 #![feature(staged_api)]
-#![feature(static_nobundle)]
 #![feature(c_unwind)]
 #![cfg_attr(not(target_env = "msvc"), feature(libc))]