fix strlcpy compile error in Ubuntu 22.04

[mverch67]

The portduino native-xxx targets do not compile on Ubuntu 22.04 (arm64), I get the following compile error:

src/mqtt/MQTT.cpp: In member function ‘bool MQTT::publish(const char*, const uint8_t*, size_t, bool)’:
src/mqtt/MQTT.cpp:476:9: error: ‘strlcpy’ was not declared in this scope; did you mean ‘strncpy’?
  476 |         strlcpy(msg->topic, topic, sizeof(msg->topic));
      |         ^~~~~~~
      |         strncpy

This is due to strlcpy (introduced in PR #8320) is not a POSIX function and not part of glibc.

However, it is contained in libbsd so this PR modifies the build command line to optionally include this library if it is installed:

!pkg-config --cflags --libs libbsd-overlay --silence-errors

Install strlcpy with sudo apt install libbsd-dev on Ubuntu if affected by this same error.

🤝 Attestations

• I have tested that my proposed changes behave as described.
• I have tested that my proposed changes do not cause any obvious regressions on the following devices:
  • Heltec (Lora32) V3
  • LilyGo T-Deck
  • LilyGo T-Beam
  • RAK WisBlock 4631
  • Seeed Studio T-1000E tracker card
  • Other (please specify below)
    • native
    • native-tft
    • native-fb
    • native-tft-debug

[jp-bennett]

@vidplace7 does this fix your compile error too?

[vidplace7]

This needs to be added to debian/control and meshtasticd.spec.rpkg as well 👍

[vidplace7]

This PR is good to merge as-is along with it's cousin #8533
I'd love to get this included in a release before we cut a Beta, since Ubuntu 22.04 / Debian 12 are currently broken 🙏