Calls to omp timing functions when _OPENMP is not defined

[rsharris]

In nttest,cpp, in the function nthashBF(), omp_get_wtime() is called even if _OPENMP is not defined.

If not having OpenMP is a supported configuration, it seems like these four calls should be redirected to some other function (get_time?) if _OPENMP is not defined.

[rsharris]

Similarly, an attempt to set up the build with ./configure --disable-openmp , suggested by ./configure --help, fails with the message "configure: error: NTHASH must be compiled with a C++ compiler that supports OpenMP threading".

[mohamadi]

@rsharris Thanks Bob for reporting these issues. I'll fix them shortly.

[mohamadi]

@rsharris just fixed the openmp issue.