Stabilize native library modifier syntax and the whole-archive modifier specifically

compiler/rustc_codegen_ssa/src/back/linker.rs

@@ -186,6 +186,9 @@ pub trait Linker {
     fn no_crt_objects(&mut self);
     fn no_default_libraries(&mut self);
     fn export_symbols(&mut self, tmpdir: &Path, crate_type: CrateType, symbols: &[String]);
+    fn exported_symbol_means_used_symbol(&self) -> bool {
+        true
+    }
     fn subsystem(&mut self, subsystem: &str);
     fn group_start(&mut self);
     fn group_end(&mut self);
@@ -724,6 +727,10 @@ impl<'a> Linker for GccLinker<'a> {
         }
     }
 
+    fn exported_symbol_means_used_symbol(&self) -> bool {
+        self.sess.target.is_like_windows || self.sess.target.is_like_osx
+    }
+
     fn subsystem(&mut self, subsystem: &str) {
         self.linker_arg("--subsystem");
         self.linker_arg(&subsystem);
@@ -1471,6 +1478,10 @@ impl<'a> Linker for L4Bender<'a> {
         return;
     }
 
+    fn exported_symbol_means_used_symbol(&self) -> bool {
+        false
+    }
+
     fn subsystem(&mut self, subsystem: &str) {
         self.cmd.arg(&format!("--subsystem {}", subsystem));
     }