Making GBBS compile with OpenMP.

[juancolx]

Before this change, the command bazel build --config=openmp //... produced the following compilation error (with g++ (GCC) 12.1.0 on CentOS Linux release 7.9.2009):

benchmarks/CycleCounting/Parallel5Cycle/FiveCycle.cc:102:1:   required from here
./gbbs/bridge.h:73:19: error: 'parallel_for_1' was not declared in this scope
   73 |     parallel_for_1(start, end, [&](size_t i) { f(i, alloc); }, granularity,
      |     ~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   74 |                    conservative);
      |                    ~~~~~~~~~~~~~

With this change, bazel build --config=openmp //... completed successfully. Then, I was able to run the BFS benchmark as follows:

$ bazel run --config=openmp //benchmarks/BFS/NonDeterministicBFS:BFS_main -- -s -src 10 -rounds 1 $PWD/inputs/rMatGraph_J_5_100 INFO: Using Bazel Remote listening on 127.0.0.1:39382 INFO: Running Bazel version 6.0.0
INFO: Invocation ID: 24ed1df9-86c0-4681-a433-f5378b838dc0 INFO: Analyzed target //benchmarks/BFS/NonDeterministicBFS:BFS_main (0 packages loaded, 0 targets configured). INFO: Found 1 target...
Target //benchmarks/BFS/NonDeterministicBFS:BFS_main up-to-date:
  bazel-bin/benchmarks/BFS/NonDeterministicBFS/BFS_main
INFO: Elapsed time: 0.102s, Critical Path: 0.00s
INFO: 1 process: 1 internal.
INFO: Build completed successfully, 1 total action INFO: Running command line: bazel-bin/benchmarks/BFS/NonDeterministicBFS/BFS_main -s -src 10 -rounds 1 /home/MY_USER_NAME/src-repos/gbbs/inputs/rMatGraph_J_5_100 1
1
2
16
52
42
11
Reachable: 125