Rollup merge of #89634 - hawkw:eliza/enable-err-warn, r=oli-obk

rustc_driver: Enable the `WARN` log level by default

This commit changes the `tracing_subscriber` initialization in
`rustc_driver` so that the `WARN` verbosity level is enabled by default
when the `RUSTC_LOG` env variable is empty. If the `RUSTC_LOG` env
variable is set, the filter string in the environment variable is
honored, instead.

Fixes #76824
Closes #89623

cc ``@eddyb,`` ``@oli-obk``

compiler/rustc_codegen_ssa/src/back/link.rs

@@ -843,19 +843,18 @@ fn link_natively<'a, B: ArchiveBuilder<'a>>(
         let msg_bus = "clang: error: unable to execute command: Bus error: 10";
         if out.contains(msg_segv) || out.contains(msg_bus) {
             warn!(
+                ?cmd, %out,
                 "looks like the linker segfaulted when we tried to call it, \
-                 automatically retrying again. cmd = {:?}, out = {}.",
-                cmd, out,
+                 automatically retrying again",
             );
             continue;
         }
 
         if is_illegal_instruction(&output.status) {
             warn!(
+                ?cmd, %out, status = %output.status,
                 "looks like the linker hit an illegal instruction when we \
-                 tried to call it, automatically retrying again. cmd = {:?}, ]\
-                 out = {}, status = {}.",
-                cmd, out, output.status,
+                 tried to call it, automatically retrying again.",
             );
             continue;
         }