[Code scan] Broadcast MD restart bool flags with the correct MPI datatype

[njzjz]

This issue is a result of a Codex global repository scan.

FIRE::restart() and MSST::restart() store the restart-file status in a C++ bool ok, then broadcast it as one MPI_INT. On receivers, MPI writes an integer-sized payload into a bool-sized object, which can corrupt adjacent stack state and is undefined behavior.

FIRE restart:

abacus-develop/source/source_md/fire.cpp

Lines 116 to 140 in 84ca04b

	void FIRE::restart(const std::string& global_readin_dir)
	{
	bool ok = true;
	if (!my_rank)
	{
	std::stringstream ssc;
	ssc << global_readin_dir << "Restart_md.txt";
	std::ifstream file(ssc.str().c_str());
	if (!file)
	{
	ok = false;
	}
	if (ok)
	{
	file >> step_rst_ >> md_tfirst >> alpha >> negative_count >> dt_max >> md_dt;
	file.close();
	}
	}
	#ifdef __MPI
	MPI_Bcast(&ok, 1, MPI_INT, 0, MPI_COMM_WORLD);
	#endif

MSST restart:

abacus-develop/source/source_md/msst.cpp

Lines 195 to 218 in 84ca04b

	void MSST::restart(const std::string& global_readin_dir)
	{
	bool ok = true;
	if (!my_rank)
	{
	std::stringstream ssc;
	ssc << global_readin_dir << "Restart_md.txt";
	std::ifstream file(ssc.str().c_str());
	if (!file)
	{
	ok = false;
	}
	if (ok)
	{
	file >> step_rst_ >> md_tfirst >> omega[mdp.msst_direction] >> e0 >> v0 >> p0 >> lag_pos;
	file.close();
	}
	}
	#ifdef __MPI
	MPI_Bcast(&ok, 1, MPI_INT, 0, MPI_COMM_WORLD);

Relevant code:

bool ok = true;
...
MPI_Bcast(&ok, 1, MPI_INT, 0, MPI_COMM_WORLD);

Suggested fix:

Broadcast with MPI_C_BOOL when available, or broadcast an int ok_int and convert explicitly to/from bool. This also makes the code consistent with the actual object size on all ranks.