sim/posix: Add the host_system interface used to execute the host command

[liqinhuixm]

Summary

Encapsulate the host system/popen interface to host_system.

Impact

We can use the host_system interface to execute the host command.

Testing

• Execute the ls, do not receive the return result of the ls command.
  ret = host_system(NULL, 0, "%s", "ls");
• Execute the ls, receive the return result of the ls command with a buffer of length buf_size.
  ret = host_system(buf, buf_size, "%s", "ls");

[yamt]

what's the expected user of this?

[xiaoxiang781216]

what's the expected user of this?

sim wifi simulation need call wpa supplicant through host_system.

[yamt]

what's the expected user of this?

sim wifi simulation need call wpa supplicant through host_system.

is it for device drivers?

[xiaoxiang781216]

what's the expected user of this?

sim wifi simulation need call wpa supplicant through host_system.

is it for device drivers?

yes, net wifi driver will call host_system("wpaxxx") to interact with host's WiFi.

[yamt]

what's the expected user of this?

sim wifi simulation need call wpa supplicant through host_system.

is it for device drivers?

yes, net wifi driver will call host_system("wpaxxx") to interact with host's WiFi.

ok. it makes sense.