remove is_bootstrap parameter (#102)

* apply openmp simd

* clean __buildin detection, moving windows build check from xgboost project, add openmp support for vectorize reduce

* apply openmp only to rabit

* orgnize rabit signature

* remove is_bootstrap, use load_checkpoint as implict flag

* visual studio don't support latest openmp

* orgnize omp declarations

* replace memory copy with vector cast

* Revert "replace memory copy with vector cast"

This reverts commit 28de4792dcdff40d83d458510d23b7ef0b191d79.

* Revert "orgnize omp declarations"

This reverts commit 31341233d31ce93ccf34d700262b1f3f6690bbfe.

* remove openmp settings, merge into a upcoming pr

* mis

* per feedback, update comments

test/model_recover.cc

@@ -96,7 +96,7 @@ int main(int argc, char *argv[]) {
   std::string name = rabit::GetProcessorName();
 
   int max_rank = rank;
-  rabit::Allreduce<op::Max>(&max_rank, sizeof(int), NULL, NULL, true);
+  rabit::Allreduce<op::Max>(&max_rank, sizeof(int));
   utils::Check(max_rank == nproc - 1, "max rank is world size-1");
 
   Model model;