Integrate Nonius benchmark into Catch2

Changes done to Nonius:
* Moved things into "Catch::Benchmark" namespace
* Benchmarks were integrated with `TEST_CASE`/`SECTION`/`GENERATE` macros
* Removed Nonius's parameters for benchmarks, Generators should be used instead
* Added relevant methods to the reporter interface (default-implemented, to avoid
breaking existing 3rd party reporters)
* Async processing is guarded with `_REENTRANT` macro for GCC/Clang, used by default
on MSVC
* Added a macro `CATCH_CONFIG_DISABLE_BENCHMARKING` that removes all traces of
benchmarking from Catch

include/internal/benchmark/catch_benchmark.hpp

@@ -0,0 +1,122 @@
+/*
+ *  Created by Joachim on 16/04/2019.
+ *  Adapted from donated nonius code.
+ *
+ *  Distributed under the Boost Software License, Version 1.0. (See accompanying
+ *  file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+ */
+
+ // Benchmark
+#ifndef TWOBLUECUBES_CATCH_BENCHMARK_HPP_INCLUDED
+#define TWOBLUECUBES_CATCH_BENCHMARK_HPP_INCLUDED
+
+#include "../catch_config.hpp"
+#include "../catch_context.h"
+#include "../catch_interfaces_reporter.h"
+#include "../catch_test_registry.h"
+
+#include "catch_chronometer.hpp"
+#include "catch_clock.hpp"
+#include "catch_environment.hpp"
+#include "catch_execution_plan.hpp"
+#include "detail/catch_estimate_clock.hpp"
+#include "detail/catch_complete_invoke.hpp"
+#include "detail/catch_analyse.hpp"
+#include "detail/catch_benchmark_function.hpp"
+#include "detail/catch_run_for_at_least.hpp"
+
+#include <algorithm>
+#include <functional>
+#include <string>
+#include <vector>
+#include <cmath>
+
+namespace Catch {
+    namespace Benchmark {
+        struct Benchmark {
+            Benchmark(std::string &&name)
+                : name(std::move(name)) {}
+
+            template <class FUN>
+            Benchmark(std::string &&name, FUN &&func)
+                : fun(std::move(func)), name(std::move(name)) {}
+
+            template <typename Clock>
+            ExecutionPlan<FloatDuration<Clock>> prepare(const IConfig &cfg, Environment<FloatDuration<Clock>> env) const {
+                auto min_time = env.clock_resolution.mean * Detail::minimum_ticks;
+                auto run_time = std::max(min_time, std::chrono::duration_cast<decltype(min_time)>(Detail::warmup_time));
+                auto&& test = Detail::run_for_at_least<Clock>(std::chrono::duration_cast<ClockDuration<Clock>>(run_time), 1, fun);
+                int new_iters = static_cast<int>(std::ceil(min_time * test.iterations / test.elapsed));
+                return { new_iters, test.elapsed / test.iterations * new_iters * cfg.benchmarkSamples(), fun, std::chrono::duration_cast<FloatDuration<Clock>>(Detail::warmup_time), Detail::warmup_iterations };
+            }
+
+            template <typename Clock = default_clock>
+            void run() {
+                IConfigPtr cfg = getCurrentContext().getConfig();
+
+                auto env = Detail::measure_environment<Clock>();
+
+                getResultCapture().benchmarkPreparing(name);
+                CATCH_TRY{
+                    auto plan = user_code([&] {
+                        return prepare<Clock>(*cfg, env);
+                    });
+
+                    BenchmarkInfo info {
+                        name,
+                        plan.estimated_duration.count(),
+                        plan.iterations_per_sample,
+                        cfg->benchmarkSamples(),
+                        cfg->benchmarkResamples(),
+                        env.clock_resolution.mean.count(),
+                        env.clock_cost.mean.count()
+                    };
+
+                    getResultCapture().benchmarkStarting(info);
+
+                    auto samples = user_code([&] {
+                        return plan.template run<Clock>(*cfg, env);
+                    });
+
+                    auto analysis = Detail::analyse(*cfg, env, samples.begin(), samples.end());
+                    BenchmarkStats<std::chrono::duration<double, std::nano>> stats{ info, analysis.samples, analysis.mean, analysis.standard_deviation, analysis.outliers, analysis.outlier_variance };
+                    getResultCapture().benchmarkEnded(stats);
+
+                } CATCH_CATCH_ALL{
+                    if (translateActiveException() != Detail::benchmarkErrorMsg) // benchmark errors have been reported, otherwise rethrow.
+                        std::rethrow_exception(std::current_exception());
+                }
+            }
+
+            // sets lambda to be used in fun *and* executes benchmark!
+            template <typename Fun,
+                typename std::enable_if<!Detail::is_related<Fun, Benchmark>::value, int>::type = 0>
+                Benchmark & operator=(Fun func) {
+                fun = Detail::BenchmarkFunction(func);
+                run();
+                return *this;
+            }
+
+            explicit operator bool() {
+                return true;
+            }
+
+        private:
+            Detail::BenchmarkFunction fun;
+            std::string name;
+        };
+    }
+} // namespace Catch
+
+#define INTERNAL_CATCH_GET_1_ARG(arg1, arg2, ...) arg1
+#define INTERNAL_CATCH_GET_2_ARG(arg1, arg2, ...) arg2
+
+#define INTERNAL_CATCH_BENCHMARK(BenchmarkName, name, benchmarkIndex)\
+    if( Catch::Benchmark::Benchmark BenchmarkName{name} ) \
+        BenchmarkName = [&](int benchmarkIndex)
+
+#define INTERNAL_CATCH_BENCHMARK_ADVANCED(BenchmarkName, name)\
+    if( Catch::Benchmark::Benchmark BenchmarkName{name} ) \
+        BenchmarkName = [&]
+
+#endif // TWOBLUECUBES_CATCH_BENCHMARK_HPP_INCLUDED