test: pass through stderr in benchmark tests

This helps a lot with debugging failing benchmark tests,
which would otherwise just print an assertion for the
exit code (something like `+1 -0`, which yields almost no
information about a failure).
PR-URL: #21860
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: Gabriel Schulhof <gabriel.schulhof@intel.com>

Author: addaleax

test/common/benchmark.js

@@ -20,7 +20,10 @@ function runBenchmark(name, args, env) {
 
 constmergedEnv=Object.assign({},process.env,env);
 
-constchild=fork(runjs,argv,{env: mergedEnv,stdio: 'pipe'});
+constchild=fork(runjs,argv,{
+env: mergedEnv,
+stdio: ['inherit','pipe','inherit','ipc']
+});
 child.stdout.setEncoding('utf8');
 
 letstdout='';