Remove popen feature in native builds

[kpu]

As we move towards repositories with models provided by other people, a yaml config file should not be able to execute arbitrary commands with a file name that begins with |

marian-dev/src/common/file_stream.cpp

Lines 25 to 37 in 08b1544

	if (marian::utils::endsWith(file, "|")) {
	#if defined(__unix__) && !defined(WASM_COMPATIBLE_SOURCE)
	auto command = file.substr(0, file.size() - 1);
	// open as a pipe
	pipe_ = popen(command.c_str(), "r");
	ABORT_IF(!pipe_, "Command failed to execute ({}): {}", errno, command);
	// there is no official way to construct a filebuf from a FILE* or fd, so we use /proc/{pid}/fd/{fd}
	// For now, this only works on Linux. There are similar workarounds for Windows.
	file_ = "/proc/" + std::to_string(getpid()) + "/fd/" + std::to_string(fileno(pipe_));
	#else
	ABORT("Pipe syntax not supported in this build of Marian: {}", file);
	#endif
	} else {

That should be disabled in consumer-oriented compiles of Marian. The feature really only seems useful for training.