cbmreco: Add option to specify OpenMP threads.

algo/base/compat/OpenMP.h

+/* Copyright (C) 2023 FIAS Frankfurt Institute for Advanced Studies, Frankfurt / Main
+   SPDX-License-Identifier: GPL-3.0-only
+   Authors: Felix Weiglhofer [committer] */
+#ifndef CBM_ALGO_BASE_COMPAT_OPENMP_H
+#define CBM_ALGO_BASE_COMPAT_OPENMP_H
+
+#include "BuildInfo.h"
+
+#ifdef HAVE_OMP
+#include <omp.h>
+#endif
+
+namespace cbm::algo::openmp
+{
+
+#ifndef HAVE_OMP
+  inline int GetMaxThreads() { return 1; }
+  inline int GetThreadNum() { return 0; }
+  inline void SetNumThreads(int) {}
+#else
+  inline int GetMaxThreads() { return omp_get_max_threads(); }
+  inline int GetThreadNum() { return omp_get_thread_num(); }
+  inline void SetNumThreads(int n) { omp_set_num_threads(n); }
+#endif
+
+}  // namespace cbm::algo::openmp
+
+#endif  // CBM_ALGO_BASE_COMPAT_OPENMP_H