bench: Suppress output when running with -sanity-check option

This change allows to simplify CI tests, and makes it easier to
integrate the `bench_bitcoin` binary into CMake custom targets or
commands, as `COMMAND` does not support output redirection

Author: hebasto

src/bench/bench.cpp

@@ -83,7 +83,7 @@ void BenchRunner::RunAll(const Args& args)
     std::smatch baseMatch;
 
     if (args.sanity_check) {
-        std::cout << "Running with --sanity-check option, benchmark results will be useless." << std::endl;
+        std::cout << "Running with -sanity-check option, output is being suppressed as benchmark results will be useless." << std::endl;
     }
 
     std::vector<ankerl::nanobench::Result> benchmarkResults;
@@ -106,6 +106,7 @@ void BenchRunner::RunAll(const Args& args)
         Bench bench;
         if (args.sanity_check) {
             bench.epochs(1).epochIterations(1);
+            bench.output(nullptr);
         }
         bench.name(name);
         if (args.min_time > 0ms) {

src/bench/bench_bitcoin.cpp

@@ -31,7 +31,7 @@ static void SetupBenchArgs(ArgsManager& argsman)
     argsman.AddArg("-min-time=<milliseconds>", strprintf("Minimum runtime per benchmark, in milliseconds (default: %d)", DEFAULT_MIN_TIME_MS), ArgsManager::ALLOW_ANY | ArgsManager::DISALLOW_NEGATION, OptionsCategory::OPTIONS);
     argsman.AddArg("-output-csv=<output.csv>", "Generate CSV file with the most important benchmark results", ArgsManager::ALLOW_ANY, OptionsCategory::OPTIONS);
     argsman.AddArg("-output-json=<output.json>", "Generate JSON file with all benchmark results", ArgsManager::ALLOW_ANY, OptionsCategory::OPTIONS);
-    argsman.AddArg("-sanity-check", "Run benchmarks for only one iteration", ArgsManager::ALLOW_ANY, OptionsCategory::OPTIONS);
+    argsman.AddArg("-sanity-check", "Run benchmarks for only one iteration with no output", ArgsManager::ALLOW_ANY, OptionsCategory::OPTIONS);
     argsman.AddArg("-priority-level=<l1,l2,l3>", strprintf("Run benchmarks of one or multiple priority level(s) (%s), default: '%s'",
                                                            benchmark::ListPriorities(), DEFAULT_PRIORITY), ArgsManager::ALLOW_ANY, OptionsCategory::OPTIONS);
 }