Rollup merge of #57650 - AB1908:master, r=petrochenkov

librustc_metadata: Pass a default value when unwrapping a span

Fixes #57323.

When compiling with `static-nobundle` a-la

`rustc -l static-nobundle=nonexistent main.rs`

we now get a neat output in the form of:

```
error[E0658]: kind="static-nobundle" is feature gated (see issue #37403)
  |
  = help: add #![feature(static_nobundle)] to the crate attributes to enable

error: aborting due to previous error

For more information about this error, try `rustc --explain E0658`.
```
The build and tests completed successfully on my machine. Should I be adding a new test?

src/librustc_metadata/native_libs.rs

@@ -163,7 +163,7 @@ impl<'a, 'tcx> Collector<'a, 'tcx> {
            !self.tcx.features().static_nobundle {
             feature_gate::emit_feature_err(&self.tcx.sess.parse_sess,
                                            "static_nobundle",
-                                           span.unwrap(),
+                                           span.unwrap_or_else(|| syntax_pos::DUMMY_SP),
                                            GateIssue::Language,
                                            "kind=\"static-nobundle\" is feature gated");
         }

src/test/ui/feature-gate/feature-gate-static-nobundle-2.rs

@@ -0,0 +1,6 @@
+//~ ERROR kind="static-nobundle" is feature gated
+// Test the behavior of rustc when non-existent library is statically linked
+
+// compile-flags: -l static-nobundle=nonexistent
+
+fn main() {}

src/test/ui/feature-gate/feature-gate-static-nobundle-2.stderr

@@ -0,0 +1,7 @@
+error[E0658]: kind="static-nobundle" is feature gated (see issue #37403)
+   |
+   = help: add #![feature(static_nobundle)] to the crate attributes to enable
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0658`.