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.

compiler/rustc_codegen_ssa/src/back/link.rs

@@ -992,12 +992,12 @@ fn link_natively(
                 let mut output = prog.stderr.clone();
                 output.extend_from_slice(&prog.stdout);
                 let escaped_output = escape_linker_output(&output, flavor);
-                // FIXME: Add UI tests for this error.
                 let err = errors::LinkingFailed {
                     linker_path: &linker_path,
                     exit_status: prog.status,
-                    command: &cmd,
+                    command: cmd,
                     escaped_output,
+                    verbose: sess.opts.verbose,
                 };
                 sess.dcx().emit_err(err);
                 // If MSVC's `link.exe` was expected but the return code