Added NOPENMP option to disable OpenMP for UMFPACK, CHOLMOD, SPQR, SuiteSparse_config (where it was just using omp_get_wtime) and GraphBLAS. Note the comments in the GraphBLAS userguide about thread-safety. If GraphBLAS is compiled without OpenMP, the #pragma omp flush in GrB_wait cannot guarantee thread safety if one user thread writes to a GrB_Matrix, does a GrB_wait, and another user thread reads that same matrix. The user application would have to ensure that the 1st thread's cache is properly flushed (perhaps with a pthreads construct). In this case, without OpenMP, thread safety is the responsibility of the user application, not GraphBLAS. Details and caveats are in the GraphBLAS user guide.