don't show the full linker args unless --verbose is passed

the linker arguments can be *very* long, especially for crates with many dependencies. some parts of them are not very useful. unless specifically requested:
- omit object files specific to the current invocation
- fold rlib files into a single braced argument (in shell expansion format)

this shortens the output significantly without removing too much information.

src/tools/run-make-support/src/external_deps/rustc.rs

@@ -325,6 +325,12 @@ impl Rustc {
         self
     }
 
+    /// Pass the `--verbose` flag.
+    pub fn verbose(&mut self) -> &mut Self {
+        self.cmd.arg("--verbose");
+        self
+    }
+
     /// `EXTRARSCXXFLAGS`
     pub fn extra_rs_cxx_flags(&mut self) -> &mut Self {
         // Adapted from tools.mk (trimmed):