added openmp_guards
Added
#ifdef __OPENMP
...
#endif
around OpenMP code, such as
#ifdef __OPENMP
#include <omp.h>
#endif
and pragma
lines
#ifdef __OPENMP
#pragma omp parallel for
#endif
This allows to build example with compilers that do not yet support OpenMP, e.g. clang. I recommend adding guards around pragma to not trigger compiler warnings, in case we want to build with -Werror
compiler flags.